I can afford it myself easily enough and the current house has quite a bit of equity in it.
The other thing I'm wondering about is when you're in a chain and want to use a new lender, are you stuck with paying ERC if the chain completes before the fixed period on the current deal or being stuck on a variable rate?
I actually had a similar situation recently. Moved into this house last August, but I had to complete my purchase 2 weeks before my fixed term ended as my buyer had a deadline to meet. My exit fee was about £2k on the ERC.
I ported my mortgage and it's remaining 2 week term over to my new house, then immediately set about trying to switch lender.
This was a headache for a few reasons and it was only by sheer determination that I solved it.
Problem 1 - Can't apply for a new mortgage at my new address when my ID documents don't match up, so I had to get a new driving license arranged ASAP to show my new address.
Problem 2 - Land registry hadn't updated to show I was the new owner of the property. This meant chasing land reg to sort it.
Problem 3 - The new lender saw my immediate mortgage exit as a sub-sale mortgage thing, which is basically where they don't like lending a mortgage on a property when it's only recently had a mortgage from another bank.
I had a lot of work to do to solve it, but in the end I spent about a month on the SVR before Nationwide finally agreed to sort it out. Still cheaper than paying the £2k exit fee to Natwest!
So in answer to your question, try and avoid what I had if you can. If you're in your fixed term deal when you complete then you may need to port it over to avoid ERC as that's calculated when you redeem it. If you're not then depending who the lender is, either stick on the SVR, get a new fix with them (then port that over) or try and get a tracker with them. Nationwide do trackers with no ERC, but from what I could see most banks had an ERC on their trackers.