UK - Public pension liabilities amounted to £1.1trn (€1.2trn) last year, according to figures published today ahead of negotiations with trade unions over changes to unfunded public pension schemes.

Tom McPhail, head of pensions research at Hargreaves Lansdowne, said figures released by the Office for Budget Responsibility (OBR) were broadly consistent with those calculated by external observers - but a far cry from the last Treasury estimate of £770bn for financial year 2008.

"It shows a willingness on the part of the Treasury to take a more realistic approach," he said.

The OBR report - containing data calculated for the first time using a 'whole of government' accounting treatment - pointed out that £260bn of the £331bn difference from the previous figure "had nothing to do with changes in the size of prospective pension payments".

Instead, it reflected a "fall in the discount rate used to convert these future payments into a one-off sum".

The change in accounting method calculates liabilities on the same basis as in the private sector, but will not be used for international comparisons.

In any case, the government's switch to the consumer prices index (CPI) inflation metric last year will begin to show in public service pension payments from this year, said the OBR - and will reduce the net pension liability when it is revalued for 2010-11.

Longer term, overall state pension costs will increase from 5.5% to 7.9% of GDP within 50 years as the population ages and second pension entitlements mature.

However, a fall in gross public service pension payments from 2% in 2015-16 to 1.4% in 2060-61 will partly offset the increase - as will the current pay freeze and planned public sector lay-offs.

Despite the OBR's nominal independence, critics pointed to the timing of the release amid government negotiations with trade unions over effective pension cuts.

The Trades Union Congress (TUC), an umbrella body, labelled the figures released as "scary but meaningless".

In a statement, TUC head Brendan Barber described their publication as "a nakedly political attempt by the government to strengthen its hand in the negotiations on public sector pensions, after its continued failure to sustain the argument that they are unaffordable".

He added: "No wonder the Office for Budget Responsibility has warned of the limitations of this approach to accounting in their report today."