Remortgaging + buy to let

[TExxx]

We're currently in the process of our buy to let mortgage going through, we have signed contract/transfer but I am wanting to remortgage our current property to borrow more as I have a few loans in my name I'm wanting to consolidate into my home mortgage, if I apply now will this affect my application on the buy to let as I don't want anything to affect it when it's taken so long to go through! Not sure if to wait until we have the house to apply or do it now to get the ball rolling as I am desperate to pay the loans off there driving me mad!

If you are going to borrow more on your main mortgage that may affect how much you can borrow on the BTL, but on the other hand if you reduce other debts that would work in the opposite direction. I probably wouldn't risk changing anything it might at the least require a re-calculation of your BTL loan, which could delay things.

Is your BTL self financing or are you topslicing?
If the latter then yes any increased lending on your residential could impact your BTL lending.

If it's self financing it should be fine. But I would still wait until it's all gone through as multiple credit checks could impact your credit score.