You've asked the wrong question OP and what works for other people isn't necessarily what is best for you.
All these 'pay down the mortgage' suggestions miss the very vital point that you are a high earner with an insufficient pension.
Therefore, you should put as much as you can into a pension for the tax relief and investment potential. This will outgrow the relatively tiny amount of interest saved by paying off the mortgage many times over. It hasn't been the case for over a decade that overpaying the mortgage will save thousands in interest, quite the opposite. I get more interest by leaving the money in my current account for a start.
I believe that you can put in up to £40k pa into a pension as long as you earn more than that. Therefore you should plan to maximise your pension contributions with a significant portion of the money over the next few years, taking your existing contributions with what you can afford to tie up until your late 50s.
Then use up your ISA allowance with an investment product with some of the money. Not all in case you need some back, but definitely some.
You will need to keep the money you intend to spend on your house in cash like savings. Some of the £100k would go nicely in premium bonds, max investment is £50k, but you could put some in DCs name if you have any.
By all means, pay down your mortgage, but only after the above. Still bear in mind that the interest rate should be less than even conservative investment growth - you should be able to get a mortgage with an interest rate of 1-1.5% and you should get 2/3 times that as a minimum over time in a low risk tracker fund.