Additional Borrowing whilst in fixed term

Dan-1987

I’m guessing this is a pretty simple one for those in the know but I’ve done some searching and can’t seem to get a definitive answer so,

We’re looking to take some equity out of our home to extend but we’re currently in a fixed deal until mid 2023,would this be possible/feasible to do,and if so what would it be referred to as? Further/additional advance? 

Anyone I know who’s done it has done so at time of changing deal/end of fixed term,which we could wait for but hoping there is another way? 

notes1

I have taken out a large long term loan secured on home with the same lender before, for work on the house. No issues. Then paid it off when next remortgaged. 

Not sure if this is cheapest or best option though. I suppose many factors come into it. 

Sofee3

We have just done this and our current mortgage is on a fixed for 3 years, it's called borrow more or further advance, you can borrow up to 85% LTV, we are with Halifax and they have a calculator which shows rough figures on what you could get.
We tried to get a 3 year deal for our extra borrowing but they only had 2 or 5 so we've gone for 5 and can hopefully match them up in 2 years. 
It was pretty hassle free, good luck!