In his statement on the BBC News website he says:
At no point did I consider myself to be in breach of the rules which in 2009 defined partner as "one of a couple … who although not married to each-other or civil partners are living together and treat each-other as spouses."
Although we were living together we did not treat each other as spouses - for example we do not share bank accounts and indeed have separate social lives.
This is simply playing with the semantics of the term partner. Many who have come to his defence in the media this morning talk about his great intellect. Surely a man of such intellect should have realised that what he was doing was at the very least bending the rules.
According to a recent article in the Times he is worth an estimated £1.3 million. If David had wanted to keep his relationship private, he should have made the decision not to claim expenses to give to his partner for rent.