A British tax on companies that shift profits out of the country and into tax havens will target inter-company fees for services such as the use of intellectual property, according to draft legislation published on Wednesday.

Companies will also be required to report their potential liability to the new tax, which will sit outside the existing corporate tax system, under the changes outlined by finance minister George Osborne last week.

Such a move could avoid legal challenges under existing tax treaties with countries such as Ireland, a major conduit for shifted profits.

Recouping cash is important to Osborne as Britain's public finances have become a major issue in the run-up to national elections in May.

Osborne said last week that he wanted to raise a further 5 billion pounds by tightening rules on tax avoidance.

Chas Roy-Chowdhury, head of tax at accounting group ACCA, said the 1 billion pounds ($1.6 billion) expected to be raised by the new tax over the next five years was modest given the size of the UK operations of the firms likely to be affected.

George Bull, a senior tax partner at accountancy firm Baker Tilly, was also surprised by the low amount.

"Perhaps [Britain's tax department] has deliberately downplayed these figures so that the move is seen less as a 'money spinner,' and more about leading the reform of the taxation of international corporates?" he said in a statement.

An opinion poll published on Wednesday showed the announcement was popular among voters, with 59 percent of respondents in a survey by polling firm ComRes for ITV News saying they were in favor of the tax.

The Treasury said the 25 percent tax would be effective from April 1, 2015, and would target conduit-type structures, such as the "double-Irish" used by Google.

In that maneuver, Google denies having a taxable presence in its main business in Britain and reports its annual UK revenue of more than $5 billion in Ireland. It then pays most of this to a Bermudan affiliate as a fee for using Google's intellectual property.

Under the new rule, the charge paid to the Bermudan affiliate could be reduced by the UK tax authority when assessing how much profit is linked to UK activities.

ACCA's Roy-Chowdhury said legal challenges to the new diverted profits tax would still be possible. "Just because the UK says the DPT is not Corporation Tax, this does not mean that other jurisdictions will accept it as such," he said.