Tyres cannot become over-inflated of their own accord, has someone recently checked the pressures and possibly over inflated them?
Be aware that tyre pressure guages can be wildly innaccurate, especially the dial types fitted to foot pumps. The best kind are the ones that are cylindrical with an indicator that pops out to show the pressure.
Tyres can of course gradually deflate and this could make the steering vague.
Also, sometimes roads get greasy when there hasn't been much rain (as if that ever happens in Britain these days) and its wise to be cautious when it rains after a dry spell: all the accumulated crud (oil, bits of rubber etc) can turn very slippery after the first bit of rain.
If you are unsure, and don't have a tame mechanic or buddy into cars, go to a tyre place or 2 and see what they say about tread depth you have left on the tyres generally. I say go to one or 2 so that you don't get an over-eager salesman telling you you need to buy a full set of the most expensive tyres they have, of course.