Erh, claiming money for a non-existing mortgage is not within the rules.
Claiming "I didn't know" won't was, won't wash, as in criminal law, contrary to politics, ignorance is no defense.
Claiming 20 grand for a residence that is already payed for (by the taxpayer) comes dangerously close to that, and there are at least 4 who have pulled that trick afaik.
Browns own 12 grand job with his brother is highly suspect.
All hail David Cameron. The people's champion.
He took the first step to see that tax payers are refunded and left the labour rabble dithering in a cloud of dust.