Nick Macpherson, the Treasury's Permanent Secretary, said that no firm has taken advantage of the scheme after Prime Minister David Cameron announced its details last year.
Of the 300 empty properties that were put forward, only four could be used - but deals for their lease have not been finalised.
Mr Macpherson said that many of the premises have been handed back to landlords or sold on because of a lack of interest.
"Of the spaces that remain, there are a variety of reasons for not being able to use them. Reasons for this include: being very small; poor condition; security considerations; restrictive leases terms preventing their use outside government; and some not being available long enough to make them viable or worthwhile for potential providers to manage," he noted.
It comes after the Welsh government announced that the Economic Growth Fund will help to create or protect up to 3,000 job roles at small firms over the coming months.
Posted by Thomas Fletcher