OP, snakes don’t just randomly enter houses. If one ever does, which is extremely rare, it’s usually looking for food like small rodents or warmth. So one of the best ways to make sure snakes stay away is to keep the house tidy, seal any cracks, and make sure you don’t have pests like mice.
If it brings peace of mind, you can fit snug door sweeps and seal gaps near the floor, not because snakes are likely to come in, but because it helps keep out all pests. I know it might feel scary, but the UK has only one native venomous snake: the adder, and even those are shy and rarely seen, let alone indoors.
There are no large or aggressive snakes in the UK, and snakebites are exceptionally rare. Deaths from adder bites are almost unheard of, and the last confirmed fatality was over 40 years ago, I believe.
I grew up on a tropical island and was quite used to seeing snakes all the time, including highly venomous ones but they do tend to keep out of humans' way. I the UK, you really don't have anything to worry about. But you can take the precautions I've stated for your peace of mind.