Postdog is correct in what he says about there being no common law marriage (although he may be a bit confused over who died).
If your friend owned the house, then it should be distributed as part of her estate (according to the rules applicable, given that she died without a will).
If your friend was the only person named/listed on the property deeds, it would be very difficult for the man to claim any share in the house. Even if he had a verbal agreement with your friend that they had an equal share in the house (due to equal contributions in mortgage payments etc), a court would be very unlikely to uphold his claim, without some formal notarised document.
The first thing her mother�s solicitor should have done was to determine who is (was) the legal owner of the house. If it was owned by your friend, then in effect, your friends mother has a non-paying tenant living in the house (who has no legal right to live there). Her solicitor should be taking the necessary legal steps to have the person evicted.
But looking at the situation from your friend�s boyfriend�s position � he has lost his partner and may now loose living in the house they shared. Perhaps they could come to some financial agreement without recourse to the courts, to ensure he was not out on the street, with nothing (which may be what the courts ultimately decide).