Depends what you use the car for, how long you intend to keep the car, and what the condition of the roads are like where you drive. It does not matter if you fit a budget of a premium tyre on a car with duff steering/suspension geometry, and with the state of the roads lately, it is hard to avoid causing this, so, if fitting expensive tyres, get the geometry checked at the same time, or, if you are a worrier, fit them anyway, what price peace of mind.
Many years ago I only ever fitted Michelins, nothing else. Brilliant tyres with roadholding that was quite something, well worth the additional cost. Then came the foreign and other brands we see now which were as good. I’ve now had all different brands on various cars over the years, one brand that did stand out for their noise reduction qualities, on a ‘W’ reg. Ford Focus, were Continentals, EcoConti if I recall correctly. My present car in regular use is a VW Golf 1.6 Tdi Blue Motion, fitted with Hankook tyres from new and quite surprisingly the front tyres covered 26,000 before replacement. I do drive fast and expect front tyres on front wheel drive cars to last far less miles. These had tread left but were proving a little ‘slippery’ on cornering so time for replacement at a cost of £68 each. My view on the importance of good tyres was gained as a motorcyclist where good tyres and performance really is essential. Basically good tyres keep you alive to ride another day, not realising this you could very easily finish up dead!
When trying to find information regarding older tyres failing the MoT I found there was a proposal to ban tyres older than 10 years on certain vehicles, mostly passenger vehicles, due to many fatal accidents where old tyres were the cause. However, I could not find anything about tyres six years’ old failing an MoT, although these were subject to the same checks as any other tyre.
There is a lot of interesting and very useful information about tyres on this website, not relevant to the OP’s location I know but very informative all the same:
This company does have a branch on the Isle of Wight and there’s plenty of useful information on their website too:
https://www.protyre.co.uk/car-help-advice/tyre-care/what-is-the-tread-depth-of-new-tyres
I have a sort of unwritten rule, Foxy: I never pay more for tyres than I paid for the car. 
My Michelin tyres are 10/11 years old and done 10,000 miles or less. I check the sidewall casings inside for cracks and they are still as brand new as the car is not left outside in UV light. Plus I am still happy at the moment doing 90 plus on them. Tracking etc never, unless needed at it has not been needed since the car was new.
As posted before, quite happy with Falken rather than Continental on the other car as I will never wear them out and they run sweet.
The rubber used for the inner-liner of a tyre is not the same as used in the sidewall on the outside Davey. For a start it will never be exposed to UV light, it’s sole purpose is to slow down the passage of air from the inside of the tyre to the atmosphere. It is generally made from a butyl-type rubber polymer. The sidewall on the outside is, most probably a 50/50 blend of 2 polymers (natural rubber and poly-butadiene rubber) that offers the best flex resistance but is rather bad where UV cracking is concerned. This is corrected for by the inclusion of chemicals called diphenylamines (sometimes you can see a purplish-brown haze on the sidewall of the tyre if too much is used).
Sorry PV, I should have posted that I inspect the inner and outer sidewalls for any form of cracking. My Brother had an advisory on his MOT on a fairly new car as he had some cracks. I took one look at it and was horrified and convinced him to buy new tyres. He then looked at mine and thought they were brand new and not 10 years plus age. Really with little wear I may not be changing them to do 600-1000 this summer. I believe legislation was brought in for coach tyres after the crash.
Yes it was and not just for coaches/buses. Truck and bus tyres (as they are known in the trade) now have a 10yr lifetime limit. After this, they must be scrapped out and recycled but no longer retreaded.