Companies that do not pay their fair share of tax should be banned from government procurement contracts, Scottish Labour deputy leader Anas Sarwar has said.

A series of household names, including internet retail giant Amazon and search engine Google, have faced accusations they do not pay enough tax.

Mr Sarwar suggests that the £10 billion spent by the Scottish public sector every year could be used to disincentivise such behaviour.

In an article in a Scottish Fabians pamphlet, Mr Sarwar argues the money could be used to drive social change as well as economic growth. He writes that rewarding firms which are seen by some as not paying their fair share of tax with such contracts is "political immorality".

Last year Amazon received £2.5m in aid from the Scottish Government.

Mr Sarwar says: "I believe there is strong public support for banning companies involved in avoiding their fair share of tax from accessing public sector contracts, bringing tax justice to public procurement."

He suggests other changes that could be driven by procurement contracts include an extension to the living wage, currently set in Scotland at £7.65 an hour.

The contracts could be used to deliver other government priorities, such as supporting small businesses.

"We have to address the issue of taxpayer-funded contracts being used to perpetuate the practices of low-pay employers," he says. "The above measures cut to the heart of the Labour movement and our political values.

"We don't just believe in building new schools or railways … and we don't just believe in re-balancing tax revenues more fairly … By carrying out these types of government interventions we are supporting people into work, we are driving up living standards, cutting down on wasted talent and giving hope to future generations."

l Public spending watchdog, the National Audit Office, has demanded greater transparency to tackle a "crisis of confidence" about the Gover-nment's use of private firms to deliver services, and urged more openness in regards to performance and profits.