London: UK Prime Minister David Cameron's electoral guru, Australian Lynton Crosby, has angrily rejected a Labour attack on his personal tax affairs as a "made up negative story".

On Thursday Labour called on Mr Crosby to explain his links to two companies based in Malta, a Mediterranean island well known as a low-tax haven for European wealth.

The Evening Standard reported Labour's claim that Mr Crosby was a director of Rutland Ltd and a shareholder in Rutland Holdings Ltd.

Both companies shared a Maltese address with Bentley Trust (Malta), a financial services firm offering "legitimate mitigation" of tax.

Labour did not accuse Mr Crosby of anything illegal.

However tax minimisation – both legal and illegal - has been a hot topic in the weeks and months leading up to May's UK general election, with the government criticised over the HSBC tax evasion scandal, and last week's debate over the arcane "non-domicile" loophole for wealthy UK residents who want to protect overseas earnings from the tax man.

Labour's Margaret Hodge, who has chased companies such as Amazon, Google and Starbucks over tax avoidance in her role as chairman of a parliamentary committee told the Standard that few people in the Conservative party wielded as much power as Lynton Crosby.

"Looking at the sheer complexity of his network of offshore interests, it is difficult to see what purpose these arrangements can possibly serve other than to avoid tax," she said.

In response to questions from the Standard, a spokesman for Mr Crosby said "Any claim, or attempt to claim, Mr Crosby has attempted to reduce his tax liability in the UK is malicious and libellous and will be treated as such."

Fairfax Media also attempted to contact Mr Crosby over Labour's claims.

He responded "seriously, you only contact me about a made up negative story placed by the Labour Party?" and did not address the specifics of the inquiry.

Fairfax Media has established through Malta's online registry of companies that Rutland Holdings Ltd and Rutland Ltd are registered at Level 7, Portomaso Business Tower in St Julian's, a town in Malta.

That is also the business address of Bentley Trust (Malta) Ltd, a company that promotes itself as "satisfying the financial needs of wealthy individuals".

It promises on its website "simplicity and peace of mind in the administration, preservation and investment of your wealth… our clients are successful entrepreneurs, professionals, business people and those of independent means".

However, Fairfax Media could not find records substantiating - or refuting - Labour's claim that Mr Crosby was linked to those companies.

Mr Crosby, along with 10 of his staff including Australian business partner Mark Textor, is reportedly working out of the Conservative campaign headquarters in Westminster, alongside 200 party staff.

His style is intensely research-driven, focusing on how to "connect emotionally" with voters and potential voters. But his political opponents have accused him of masterminding negative and personal political attacks.

The attack on Mr Crosby came in a week that Labour extended its election lead on the Conservatives in two polls.

Labour's promise on "non-dom" tax proved popular in some polls, however Labour's shadow chancellor Ed Balls was revealed to have opposed the idea only a few months ago, saying it "would cost Britain money".

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