When movie moguls set out to shoot a British film, accents, costume and scripts count for nothing.

Instead they must rigidly stick to a complex mathematical formula drawn up by the government and defined in traditionally impenetrable legalese.

The Oscar nominations given to a rich handful of British-style films, including Shakespeare in Love, Little Voice and Elizabeth, was of course good for British national pride. And Shakespeare in Love getting the award for best picture was the icing on the cake.

American Gwyneth Paltrow: Star of the British film Shakespeare in Love

But things are not always what they seem in an industry that thrives on multi-national co-operation and deal-making.

Which helps explain why the 1995 dramatisation of Jane Austen's classic English novel Sense and Sensibility, featuring all-Brit stars Emma Thompson, Kate Winslet, Alan Rickman and Hugh Grant, was not a British film.

However, another motion picture from the same year, Judge Dredd, which stars the all-American action hero Sylvester Stallone and is set in a the proto-American Mega City One, was British.

Raft of incentives

For British film-makers - fed up with reports of the death of the British film industry - there is an obvious desire for the fruits of their labours to be seen as the production of their home country.

But there are other incentives as well. Film-makers seek a "British classification" because of the tax breaks, lottery money, government grants and EU aid. That means playing by the government's rules.

The detailed criteria set out in the Films Act 1985 mean that 92.5% of a film's running time is created in Britain. The remaining time may consist of "[film shot] or sound recordings made" in a studio in Ireland or a Commonwealth country.

Hugh Grant: A Briton in the American film Sense and Sensibility

There is also the proviso that the film must be made by a British or European registered company, and a rule that the vast majority of labour costs must go to citizens of Britain, Europe or the Commonwealth.

These regulations are in the process of being modified, in an effort to widen the net for British classification.

Culture Secretary Chris Smith has approved a scheme that will be based on how much money is spent in Britain, rather than studio use.

Hollywood studios qualify

The plans, currently being pored over by Brussels, mean that in future a British tag will be granted if three-quarters of the movie's production budget is spent in the UK, and most of the actors and crew are British, European or from the Commonwealth.

Hollywood studios with a subsidiary in Britain will qualify. The rules will be relaxed if most of the groundwork for the film is done in the UK or if at least half the technical equipment used in production is British.

While the new rules should help foster more British films, there looks to be no let-up in the mind-boggling task of ensuring a UK classification. Considering the manpower it must involve, it's no wonder the closing credits are always so long.