l What tax changes are being made as a result of the new Scotland Act?

The Scottish Government will become responsible for raising about half the income tax generated in Scotland from 2016 as its grant from Westminster is cut. The move is designed to make MSPs more accountable for the cash they spend. Stamp duty and landfill tax will be abolished in Scotland in 2015 and Holyrood will devise alternatives.

l Why is HMRC collecting Scottish income tax?

The Scottish rate of income tax will remain part of the UK tax system, so the UK taxman is responsible for collecting it. A "Scottish taxman", Revenue Scotland, is being set up to collect the new versions of the fully devolved stamp duty and landfill tax.

l Why are MSPs concerned?

HMRC is accountable to Westminster. But any errors it makes on SRIT would impact on Scotland's budget – and could even benefit the rest of the UK at Scotland's expense. So MSPs want to ensure they can haul HMRC officials before Holyrood's audit committee to explain themselves if things go wrong.

l What could go wrong?

Major public sector IT projects have an unhappy history.