(2-part post):
Just for a moment, forget about the will. If the deeds to your house show that you owned it as 'joint tenants' then it was your legal partnership that owned the property. Upon your husband's death you, as the surviving partner, automatically became the sole owner of the property. (If your husband's will had stated that his share of the house should go to Battersea Dogs' Home, that part of his will would have been invalid because neither of you owned a distinct share of the property; it was your partnership which owned all of it)
However if the deeds show that you were 'tenants in common' then you both owned a distinct share of the house (which would be one half each unless stated otherwise). So your husband had the right to leave his share of the house to whomever he chose (which, fortunately from your point of view, was not Battersea Dogs' Home!).
If you were joint tenants the house is already yours. All you need to do is tell the Land Registry is that your husband has died. Simply download, print and complete this form:
http://www1.landregis.../public_guide_009.pdf
Then send it, with a copy of the death certificate to the relevant Land Registry office for your area:
http://www1.landregis...nal/areas/default.asp