Buy To Let - remortgage my house?

BTL_Reading

Hi, I'm considering getting into buy-to-let, I have I think most of the deposit cost for buying a flat and so will be looking into BTL mortgages which I'm aware are very different from a standard mortgage for a primary residence.

However, I've paid off the mortgage for the house I live in and it's value is significantly more than the flat I would consider buying to let.

So are there any prohibitions against remortgaging my house in order to pay for the flat outright, and if so, could I part-remortgage in order to raise the rest of the deposit (or get a better rate) for a BTL mortgage for the flat?

Are there specific differences in tax implications depending on which property the debt is on?

If I get further into this I'll be talking to mortgage brokers directly, I'm just interested in the general opinion about this so I know where I stand.

If it's significant, I don't have dependents so not too concerned about issues like inheritance tax, and if I should die with a large mortgage pending on my house, there's no-one who's going to be left homeless if it's sold off to pay the mortgage.

Thanks.