An empty main residence, now how can that be?

I just can't think of an explanation for this series of events.

Labour MPs Ann and Alan Keen claim £137,679 for a second home near Parliament, declaring their main home to be Brentford, a massive 10 miles from the Houses of Parliament.

Now Hounslow Council have written to the troughing couple telling them that "urgent action" is needed to explain why their main home in Brentford is unoccupied. Apparently they "have been given a month to stop their local council repossessing their home... If the council does not get a satisfactory response from the Keens, it then has the power to issue an Empty Dwelling Management Order which would allow the council to take possession of the property and bring it back into use."

I just don't understand what this all means...