A firm based in an offshore tax haven stands to make millions of pounds in profit from a public private partnership (PPP) deal to refurbish schools in the Highlands.

3i Infrastructure Ltd, an investment company registered in Jersey, has a 50% equity stake in the consortium behind the 11-school plan.

But the firm will pay no UK tax on any profits made from the schools as its assets are held offshore - beyond the reach of the Treasury.

The situation has prompted critics to claim PPP is helping companies avoid paying their fair share of taxation.

A UK newspaper last week revealed how companies involved in PPP had set up overseas investment vehicles for tax efficiency purposes.

Under PPP, which was introduced by John Major's administration and pursued vigorously by the Labour government, a private contractor builds and operates a school or hospital in exchange for charging the relevant public body for use of the facility.

The system, which has been used for dozens of capital projects in Scotland, has attracted critics who believe it is poor value for money and results in the construction of poor buildings.

One of the deals in Scotland - a £134 million project to build and refurbish 11 schools in the Highland Council area - is likely to benefit an offshore company that does not pay tax in this country.

The consortium formed to run the project, Alpha Schools (Highland) Limited, is a British registered company and liable for UK tax. But one of the firms with a 50% equity stake in Alpha is 3i Infrastructure Ltd, a Jersey-based outfit.

The company, which was listed on the London Stock Exchange last year, has committed about £7.9m to the project.

3i's website states the firm invests in "assets that are at an early stage of development, most likely to be PFI/PPPs where the potential for capital growth exists, but yields tend to be limited until operational ramp-up".

The same site flags up an interest in "assets, including PPP projects and privatisations, that are undergoing a period of operational ramp-up following construction, and which generate yields and also capital growth".

3i Infrastructure's income amounted to £20.7m for the nine months up to September 2007, while its gain on investments totalled £21.2m.

The Jersey link is controversial as Treasury rules state that government departments should pay attention to the "propriety of tax arrangements" of firms entering into PPP deals.

A spokeswoman for 3i Infrastructure said: "Alpha Schools is a company registered in the UK and liable to UK tax. It has two main shareholders: 3i Infrastructure Limited and Galliford Try - a leading construction firm.

"3i Infrastructure is a Jersey-based investment company. However, the PFI companies in the portfolio of that company are registered and taxed in the UK in the normal way. The post-tax profits from these PFI companies are simply aggregated by 3i Infrastructure, before being passed on to investors."

Councillor Bill Fernie, the Chairman of Highland Council's education, culture and sport committee, said of the 3i link: "I know nothing about that. How Alpha Schools is made up I don't know."

A spokesman for the SNP said: "This new information is yet another argument against PFI, and the excessive profits that are part and parcel of it. It demonstrates exactly why we need to move towards the Scottish Futures Trust alternative that the SNP government is developing."