Be careful David - In my experience, tyres can be well within the legal limits but I found they will easily aquaplane if you run into extrememly heavy rain.
I recall heading into London on the M40 and found myself aquaplaning going up hill at the Stokenchurch cutting. My tyres were well worn but were still quite legal and I wasn't driving at excessive speeds as it was a known accident black-spot even in the dry.
From then on I have always changed tyres sooner rather than later.
EXAMPLEWhile on this subject, there is also a very good argument for always putting your best tyres on the rear. There are plenty of You-tube videos about this; the best one was a Top Gear video (I think) which frustratingly, I can no longer find.