Repossession without arrears after property turned into cannabis farm?

My mortgage company are intending to sell my buy to let property without my permission citing a breach of the mortgage. I have owned the house since 2003 but in 2011 the house was turned into a cannabis farm by rogue tenants resulting in an estimated repair bill of £20,000 which I simply do not have.

I have continued to make all mortgage repayments and carry out essential repairs and maintenance, but because it has been untenanted for almost three years the lender is now seeking to sell the house under the law of property act 1925.

I only discovered this fact when a specialist receivership company rang me to arrange access for a valuation of the house. The property will clearly have substantial negative equity so In these circumstances can the mortgage company rub further salt into the wounds by coming after me personally for any shortfall.

Peter