If England’s rugby players felt like long shots before their shock win against their all-conquering Irish counterparts at Twickenham on Saturday evening, they might have spared a thought for Britain’s National Hunt trainers approaching Tuesday’s start of the Cheltenham Festival.

There are 28 races at the showpiece event of the jumping season and only two favourites – for the Plate Handicap Chase on Thursday and the Triumph Hurdle the following afternoon – are stabled in British yards. As if that were not ominous enough for the home side, Nicky Henderson – the only British trainer to put up anything more than token resistance to the annual Irish invasion in recent years – goes into the meeting with Constitution Hill, his stable star, on the sidelines and the rest of his string a long way short of its usual form.

Related: Willie Mullins: ‘Is this the year we have a blowout at Cheltenham? The expectation is so heavy’

No one seems to mention the Prestbury Cup any more, perhaps because the Irish are 1-16 to outscore the home team for the eighth time in the past nine years (the other year was a 14-14 draw). Three years on from the extraordinary Festival when Ireland claimed 23 winners, Paddy Power offers just 7-1 that they will match or surpass that record total.

Most punters care little or nothing about where the horses they back munch their grass, so long as they cross the line in front. But Ireland’s increasingly entrenched dominance at Cheltenham is a cause for concern not just for the British Horseracing Authority but, some may be surprised to hear, its Irish counterpart too.

“The biggest threat to Irish jumps racing is the demise of British jumps racing,” Jonathan Mullin, Horse Racing Ireland’s new director of racing, said this past week. “This trajectory [for British jumping] isn’t good for anyone. That’s the reality.

“The health of the National Hunt scene [in Britain] is a massive issue for Ireland. We have a vested interest in it being in better health. That’s not to say that ours doesn’t have issues as well, and we need to fix them or create an environment where they can fix themselves, but they need to get healthier together.

“There are a huge number of breeders in Ireland, many of them National Hunt, and some will be career breeders and some will be dairy and sheep farmers with mares. They’re making decisions every year to put mares in foal and prepare horses for sale and the vast majority of that market is British.”

By many measures – including total prize money, turnover, attendance, the number of races and horses in training – the British National Hunt industry is much bigger and richer than its Irish counterpart. For decades, that imbalance was ­generally reflected in wins at the Festival and there was a nadir in the late 1980s when a single Irish winner was not a given.

The subsequent greening of the Festival economy has been remarkable and, in recent years, relentless. Even a decade ago, Irish-trained horses made up 25% of the fields. In the past two seasons, they have been in the majority – 55% in 2022 and 53% last year – and could well nudge 60% this year.

Some will say that it is all – or mainly – down to one man: Willie Mullins, who is odds-on this week to have the half-dozen victories he needs to be the first trainer to reach 100 Festival winners. Mullins’s talent, determination and graft over 30 years have certainly taken him to a point where his iron grip on the market for young horses, from France in particular, means that every new recruit will have a big-money buyer ready and waiting.

Kelso 1.35 Glorious Lion 2.10 Go Boy 2.45 Going Mobile 3.20 Imperial Merlin 3.55 Myretown 4.30 Eloi Du Puy

Warwick 1.50 Billytherealbigred 2.25 Doyen Quest 3.00 Zonda 3.35 Anti Bridgie 4.10 Sporting Ace 4.45 Astronomic View 5.15 Valgrand

Southwell 4.50 Starshiba 5.25 Red Scotch 6.00 Prince Eric 6.30 Sixties Chic (nb) 7.00 King Of York 7.30 Stoic Syd 8.00 Heerathetrack 8.30 True Courage (nap)

But Mullins was just one among nine Irish trainers – another record – who saddled at least one Festival winner last year, while no fewer than 36 Irish yards sent at least one horse to the meeting. Though his 33 winners in the past five years is a long way ahead of Henderson’s 13, Gordon Elliott (15) and Henry de Bromhead (16) have also fared better than Britain’s leading trainer in that time. Mullins may be steering the green bandwagon but he is far from the only trainer aboard.

A review of British jumping after Ireland’s 23-winner Festival in 2021 aimed to make the programme more competitive and persuade major British owners to keep their horses at home. “It is early days and there are interventions all the way through breeding in terms of incentives for British-bred horses and retaining your horses here in training,” Julie Harrington, the BHA’s chief executive, said this past week. “But we’re not naive. We know the decision of many owners is to place their horses with who they would consider in-form trainers.”

British jumping, in other words, is going to get another almighty beating at this Cheltenham Festival, and no doubt several more after that. It is only the scale of the embarrassment that has yet to be decided.