The Liberal Democrats have called for tougher safeguards to prevent companies gaining a commercial advantage by sponsoring government departments.

The party's deputy leader, Alan Beith, claims that rules are being broken or ignored in a number of cases and that the potential dangers of conflicting interests are often not known.

Most government departments receive sponsorship, with an obligation to declare any amount totalling �5,000 or more.

The Lib Dems are not claiming that donations have bought favours, but they are calling on ministers to tighten the rules in order to reassure the public.

Regulations prevent departments from accepting sponsorship from firms involved in significant commercial negotiations with them.

However, the Liberal Democrats claim some departments are breaking those rules or ignoring them.

They point out, for example, that the Department of Culture, Media and Sport has been sponsored by the BBC, Channel 5, Sir Cameron Mackintosh and the Granada group.

They claim all of these parties are potential beneficiaries of the decisions taken by the department.

It is not the first time sponsorship deals have raised concerns.

Three years ago, the parliamentary watchdog investigated the "dangers" of government departments accepting sponsorship from major corporations.

Political embarrassment

Donations to political parties have also come under scrutiny, with new regulations being introduced last year.

The rules forced political parties to disclose publicly donations of more than �5,000 and introduced a ban on foreign donations and a limit on the amount each party can spend on a general election.

Prime minister Tony Blair came under scrutiny after it came to light that Formula One boss Bernie Ecclestone gave a �1m donation to the Labour party in 1997 before the May election.

Bernie Ecclestone's �1m gift caused trouble for Labour

Mr Blair faced allegations that the money had influenced the government's decision to seek an exemption later for Formula One from a European tobacco advertising ban.

Amid public pressure, the party decided to return the money.

Two months ago, the Labour Party announced it was setting up a new committee to vet future donations in the wake of allegations of "cash for questions" over its acceptance of a �100,000 donation from adult magazine publisher Richard Desmond.

The new six-member fundraising committee will oversee any gift of more than �5,000.

Future donors will have to agree to a statement accepting they were not giving the money "for commercial advancement or advantage for themselves or others".