Hello and thanks for using Just Answer.
I am Al and am happy to assist you with your enquiry.
Nearly all Lenders will grant a Buy to Let 80% mortgage, so that the customer has at least 20% equity left over. Therefore, you should be entitled to get a Mortgage for £100,000.
Unless you are staying with your existing Mortgage Lender, you could try the Mortgage Works as your new Lender.
I hope this helps and answers your question.
I'm not in any way associated with the Mortgage Works- it is just that most of my BTL clients seem to obtain Mortgages from them and they are probably the most popular buy to let provider.
Can I asssit you any further?