The MLA also disclosed that the rental expenses he and First Minister father claim from the Assembly for the premises will add up to "at most" £56,000 per year.

He disputed reports that their combined total was £62,000, but the figure is still greater than sums claimed by other MLAs.

Mr Paisley Jnr said his father-in-law replaced developer Seymour Sweeney as sole director of the firm that bought the building last year.

While he has stressed that Mr Sweeney received no rent from the property, the link has reignited controversy over the MLA's long-term lobbying for the businessman.

Stormont sources were last night questioning his future as a Minister, despite the continued support of his father. One DUP Assembly source told the Belfast Telegraph that the party was "sick to the back teeth" of the situation.

MLAs are permitted to receive money for offices owned by family members, and Mr Paisley Jnr is by no means the only Ulster politician to have made such rental claims.