Embattled Labor backbencher Craig Thomson has come under further pressure over the use of his Health Services Union credit card to pay for escort services while he was the union's national secretary.

The Opposition is ramping up pressure on Mr Thomson over the case, attempting to force him out or trigger a by-election to bring down the Government.

Mr Thomson, Labor member for Dobell on the NSW central coast, has been accused in Federal Parliament and in Fairfax newspapers of using a union credit card to pay for prostitutes.

During defamation proceedings begun by Mr Thomson against Fairfax in the NSW Supreme Court, credit card vouchers with Mr Thomson's signature, phone records and his driver's licence details were alleged to reveal how he had used his union credit card to pay escort agency services in April 2005.

"Yes, I authorised all the credit card bills," he told radio 2UE two weeks ago.

However he said it was not him that used the card for prostitutes, and said another man - who he would not name - had incurred the charges, forged his signature but later paid money back to the union.

"The union reached a settlement with another gentleman who paid back $15,000 in relation to use of credit cards at an escort agency," he said.

Yesterday, Prime Minister Julia Gillard defended Mr Thomson, saying she has full confidence in him and looks forward to continuing as the member for Dobell "for a very long, long, long time to come".

If Mr Thomson resigned from the marginal seat and it fell to the Coalition, Ms Gillard's minority government would fall.

Now, News Limited newspapers have reported the ALP bankrolled some of Mr Thomson's legal action against Fairfax - which was later dropped by Mr Thomson - with up to $90,000 of ALP funds.

And Mr Thomson has now added an entry to his registry of members' interests, saying: "In May 2011 the Australian Labor Party (NSW Branch) paid a sum of money in settlement of a legal matter to which I was party."

Today shadow attorney-general George Brandis told the Senate there were a number of undisputed facts that were now public.

"That on two occasions, on April 8, 2005 and August 16, 2007, calls were made from Mr Thomson's mobile telephone to the telephone number of Sydney Outcall, an escort agency.

"That on April 9, 2005 and August 16, 2007 the HSU (Health Services Union) credit card issued to Mr Thomson was used to pay for services provided by Keywed Pty Ltd, which is the corporate entity which trades as Sydney Outcalls."

He said the payments were in the amounts of $2,475 and $385 respectively, and the credit card vouchers were signed in Mr Thomson's name and Mr Thomson's driver's license number was endorsed on the receipt.

Signature

Senator Brandis said Paul Westwood, a handwriting expert and former head of the document examination section of the Federal Police, has concluded the signature on the credit card voucher and Mr Thomson's drivers license were made by the same person.

"If Thomson did not sign the credit card voucher then it was signed in his name by an expert forger who eluded Mr Westwood and who also had Thomson's driver's license," he said.

Senator Brandis asked how could Mr Thompson's credit card, driver's license and mobile phone "find their way into the possession of another person".

He said that in April 2009 the Sydney Morning Herald reported Mr Thomson obtained cash advances on the HSU credit card totalling more than $100,000.

"An external audit has not been able to locate any receipts or other records to justify those cash advances. Those matters, I understand, are currently being investigated by Fair Work Australia," he said.

Legal costs

On the $90,000 reportedly paid by the ALP to bankroll Mr Thomson's discontinued defamation case against Fairfax, Senator Brandis said it was only yesterday that Mr Thomson amended his register of members' interests to include a payment by the ALP.

He said Ms Gillard should thoroughly investigate Mr Thomson's conduct.

"Why does she continue to believe that the conduct of the Member for Dobell is acceptable and how can she possibly continue to assert that he is doing, in her words, a fine job?"

Later, Ms Gillard told Parliament that she has been told by Mr Thomson the media reporting on the register of members' interests is incorrect.

"His statement of interests was updated in the interests of full disclosure," Ms Gillard said.

"I have complete confidence in the Member for Dobell."