If you pay for advice they will say it depends on your 'attitude to risk' what you do with spare money.
A safe bet is a NEST pension or similar as they have lower charges, the advantage of a pension is that if you pay in £100 the government put 20% or so, so that's free money. Time spent in the market is important and at 40 you have time for your money to grow
I have some of my Emergency money in Vanguard S & P 500 fund as that has really grown well historically.
Another worthwhile thing is overpaying your mortgage a bit once you have about 6 months in bills saved up, I saw my mortgage as a debt and always overpaid and have never regretted it.
Those are all low risk options, there is probably more money to be made if you are willing to risk some or all of your money
Glad to se someone thinking about the future so many just spend what they earn, when things are going well and then when they get older they have nothing to fall back on, having said that try and enjoy yourself as well,,