David Cameron’s speech today on the cost to the NHS of the misuse of alcohol makes an important break with past claims on the subject.

In line with new guidelines that only primary diagnoses fully or partly related to alcohol will in future be counted, he says correctly that there were 200,000 hospital admissions in England in 2010-11. (He means 2009-10.) This is in sharp contrast with recent figures (repeated today by The Guardian) that the total is over a million.

I have explored before why this change has come about. There is little doubt that the industry pressed for it, as the previous indicator exaggerated the true total, while its dizzying rate of growth was largely an artefact of hospital coding practice.

However, Mr Cameron then goes on – according to the No 10 Downing Street press release – to say that the total cost of alcohol to the NHS in England is £2.7 billion a year. This figure was worked out by the Cabinet Office in a 2008 report and appears once again on page 63 of Statistics on Alcohol England 2010-11, published by the NHS Information Centre in May 2011. So it seems reasonable to assume that this was Mr Cameron’s source.

But this figure was worked out using the old method of calculating admissions, not the new one. It estimates the cost of admissions directly and partly attributable to alcohol at £1,189.6 million, based on 802,066 admissions, which was the most recent figure available when the Cabinet Office made its calculations.

The actual admissions figure for the latest available year, as Mr Cameron said, is 200,000. (He says this is for 2010-11, but the latest figures available are for 2009-10, and amount to 194,800, near enough 200,000.) So that item in the cost table should have been reduced proportionately, from £1.2 b to around £290 million in 2006-07 prices – rather more in today’s prices.

It is also unclear where Mr Cameron gets his figure for the cost of A&E visits, which he says was £1 billion. The Cabinet Office/NHS IC table (below)  lists this at £645.7 million in 2006-07 prices. There may be evidence of an increased burden on A&E departments since then, but if so I’m unaware of it.

The upshot is that his estimates of the cost to the NHS are exaggerated by just under a billion pounds, or rather more than a billion if the A&E figure can’t be justified. Instead of £2.7b, the right figure is in the region of £1.5-1.8b.