Somerset have never won the county championship but they secured their position as everyone’s second favourite county when they defeated the reigning champions Surrey with less than five minutes to spare and closed the gap to eight points with two matches to play.

These two counties are also drawn against each other in the first of the Vitality Blast T20 semi-finals at Edgbaston on Saturday, which becomes a spicy prospect. After this victory over Surrey by 111 runs, Somerset will have a higher morale.

Somerset’s two match-winners were their two spinners who took all 20 of Surrey’s wickets. One, predictably, was their left-armer Jack Leach, who has returned to England’s squad for the tour next month to Pakistan. The second, less so, was Archie Vaughan, the 18-year-old son of the former England captain Michael.

The younger Vaughan had never taken five wickets in an innings in any format by his own admission, having represented England Under-19s as a batsman. He took six wickets for 102 in Surrey’s first innings and five for 38 in their second for match figures of 11 for 140.

Somerset’s captain Lewis Gregory said: “To get a win with only a couple of minutes left in the match was very special. Four-day wins are some of the most pleasing you have as a cricketer because you work so hard for them.

“Archie has taken to first-class cricket like a duck to water. The fact that he is more of a batter than a bowler is the really exciting bit and we believe he is going to be very good to watch with the bat over a number of years. If you throw in the off-spin he has bowled in this game, there is a mighty special cricketer developing.”

The joke was therefore soon circulating in the West Country: that Shoaib Bashir is England’s first-choice spinner but now Somerset’s third-choice.

Outstanding features of Vaughan’s off-spin were his unrelenting steadiness, accuracy and patience. Leach is renowned for being steadiness itself, but his partner – 15 years younger – was no less so in the course of his 69 overs with barely a long-hop.

But not the least bizarre feature of this epic game was the sight of Tom Banton charging out to celebrate with his team-mates on one leg at the end. Banton had severely damaged his left ankle in a football warm-up on the third morning; but, such is the commitment to red-ball cricket and his county, that the player who had been a T20 England and franchise star in the making made two match-winning contributions, his 46 on one leg following his first innings of 132.

Towards the close of day three the central figure had been Shakib Al Hasan, the Bangladesh all-rounder, who had Somerset’s second innings on a string. Shakib, as a left-arm spinner, has taken 242 Test wickets and scored more than 4,500 runs. Surrey signed him for this single game, in the hope of preventing Somerset gaining ground on them, for a hefty five-figure sum.

Somerset were 153 for nine, only 149 ahead, when Banton hobbled out with a runner to join Craig Overton on the third evening. They defied Shakib until the close, and on the fourth morning Banton played some remarkable shots – including a reverse-sweep – without putting any weight on his front foot or left ankle. Together they added a crucial 71 for Somerset’s last wicket, before Shakib bowled Banton, which set Surrey 221 to win at three runs per over.

Surrey flew in Shakib from Bangladesh. Somerset brought in Vaughan from Bridgwater. Since leaving Millfield he had played for their club, and debuted for Somerset in the one-day Metro Cup and one championship game. For his second match against Surrey, who are aiming to make it a hat-trick of championship titles, he was asked to open the batting – and scoring a valuable 44 on the first morning – before being required to partner Leach.

Surrey made the mistake of not trying to score any runs, simply intent on surviving and blocking for a draw. But Vaughan soon nipped in to dismiss two of their left-handers, the captain Rory Burns and Ryan Patel, with classic off-breaks.

Thanks to two former England players well known for their defensive skills, Dom Sibley and Ben Foakes, Surrey seemed to be on course for a draw at 95 for three with fewer than 20 overs left. But a collapse set in and they were soon resorting to the tactic of sending on substitutes with drinks and towels, even though it was a crisp sunny evening, to make sure Somerset did not squeeze in extra overs – above 15 per hour – before the 5.30pm close.

Surrey pair did not score off 78 balls

Leach did Vaughan, and the rest of his team, a favour by dismissing the two right-handers, Sibley after a 183-ball vigil and Foakes with balls that turned to flick their outside edges to be caught by Somerset’s captain Lewis Gregory at slip. Vaughan, pitted against another left-hander in Shakib, had him caught at slip too, then bowled Tom Curran off an inside edge and pinned Cameron Steel leg-before, bowling round the wicket with unflagging accuracy on a pitch that offered turn but at no great pace.

Jordan Clark, one of the biggest T20 strikers of a white ball, blocked in company with Kemar Roach. Surrey’s ninth-wicket pair did not score a single run off 78 balls. Overton was on his knees at second slip literally – his team-mates only metaphorically – in the fielding position pioneered by the former Somerset and England player Marcus Trescothick.

Overton even tried Stuart Broad’s trick of turning the bails round – and it worked.

Leach finally nipped in to have Clark caught behind off yet another forward push then pinned Dan Worrell leg-before with his second ball, a quicker one. The home team celebrated, including Banton, who would have won a one-legged race.

Meanwhile, Matthew Potts took nine Lancashire wickets in one innings for 68 runs to record the fifth-best figures for Durham, who won by an innings and 63 runs

Potts was dropped for the third Test against Sri Lanka last week, but was then named in the England party for Pakistan.

While Ben Stokes was having a lengthy batting net at the Riverside, which suggests he will be fit to play in the first Test against Pakistan next month if not to bowl, Potts recorded his career best in one innings and match figures of 12 for 126.

“That feels really good,” Potts said. “It was great to come back and deliver for the boys at the end of the season. I felt that was only right that we turned up to do the job.”

Potts added: “David Bedingham [who made Durham’s highest-ever score of 279] keeps churning them out and both he and Colin Ackermann are very chilled at the crease. They had a good tempo and put the bowlers under pressure [in a record stand of 425] and that was the way to go on that pitch.  I think that’s where Lancashire went wrong in their approach in the first innings.

“It was a pretty flat pitch and that made it hard work. We thought it was going to be a full day but it just so happened that we got an opening and took the chance to push on.

“Scott Borthwick [Durham’s captain] told me after my sixth over that it was time to put my feet on ice but I got a wicket and he said: ‘OK, I’ll leave you on,’ and I said ‘Good luck taking me off’, but after my 10th over I was absolutely goosed. I’d thrown everything I could at them.

“I took the second new ball and threw the old one as far as I could off the field. It’s a disgusting thing, I’ve got it in my pocket and it looks as though I’ve been throwing it for my dogs for the past hour.”

Potts was recalled to take the last Lancashire wicket – and his last for Durham this season because he now has to join England’s one-day squad to play Australia.

The only good news for Lancashire, who took a point from the game, is that fellow strugglers Nottinghamshire were also beaten by an innings by Essex. Lancashire and Notts are battling to avoid joining Kent in getting demoted.