I've got through a little research into the difference(s) in handicap marks between the UK and Ireland.
It's obviously a very limited sample. Really all I did was look back through paper-copy of advance entries for some races and check the figures against the official Irish ratings.
Horse | Code | Ire | UK | Diff |
Chef Des Obeaux | ch | 149 | 149 | 0 |
Cabaret Queen | ch | 142 | 145 | +3 |
Moonshine Bay | ch | 139 | 140 | +1 |
Noble Endeavor | ch | 131 | 140 | +9 |
Scoir Mear | ch | 128 | 130 | +2 |
The Jam Man | hd | 143 | 144 | +1 |
The Trigger | hd | 85 | 105 | +20 |
The Trigger | ch | 95 | 115 | +20 |
Sir Ector | hd | 90 | 105 | +15 |
Safe Home | hd | 86 | 88 | +2 |
Borice | hd | - | 147 | - |
Borice | ch | 146 | 146 | 0 |
Cartwright | hd | - | 137 | - |
Thosedaysaregone* | hd | 126 | 132 | +6 |
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I highlighted Thosedaysaregone for a number of reasons. The 6lbs differential matches the notional idea I've had of the differential for a long time but it's the only one that does. Also, its figures relate to its situation before it won the big race in Ireland recently. It was entered at Ascot that weekend where its mark was 6lbs higher than in Ireland.
This is why I often claim that UK horses - at least those in the same ball park as the likes of TDAG - will be badly handicapped if they set hoof in Ireland, whereas those nearer the top wouldn't be relative to horses of similar ability but they would be relative to horses much further down the weights.
I know that the marks of horses rated 150+ are supposed to be 'harmonised', ie agreed between the two handicappers but the respective ratings for The Trigger and Sir Ector would point to quite a discrepancy.
For the Festival, though, I don't imagine many horses in the bigger handicaps will be rated below the mid-130s so the huge discrepancies probably won't arise. However, maybe races like the Fred Winter and M Pipe could be there for the Irish horses to exploit if the UK handicapper doesn't raise them too much from their Irish marks.
I suspect, though, there's a lot more to it than that.