Taken a more detailed look at what I've got following builders' re-quote and my conclusion is it's definitely not enough to do loft now after mortgage, and I don't think it's worth leaving a bit of mortgage outstanding to potentially pay for it, as it would still be quite a lot if we wanted to have a safety buffer (at least 10% extra for fuck-ups and 'we might as well do that while we're at it' plus a enough to decorate bedroom and fit and decorate a bathroom). Unless financial adviser has a very good reason I think that makes it a firm case to pay off 100% and then have a think about what we do with the rest intelligently.
You seem to have received some bad financial advice on this thread.
People seem to have an obsession with paying off a mortgage. The key factor is the interest rate of your mortgage versus how much you can get in an instant access savings account. For some, especially those that remortgaged during historic interest rate lows, you would be better off keeping the money in the bank.
I’m also sceptical of the need to see a financial advisor, but since its unlikely anyone will listen to me on the first point, pretty pointless to get into it on the second.