Another vote for Altberg boots.
It depends how serious a walker you are now or intend to be in the future? If the three peaks challenge next year is just going to be a one off thing it's probably not worth spending loads of money on boots.
If you intend to walk regularly and if your budget allows and the best possible quality, fit, comfort and durability are top of your priority list I would recommend that you look at the following models of Altberg boots. They're definitely not cheap but quality never is but if you look after them properly they will last you a long time. All Altberg boots can be resoled by the factory if and when the need arises.
2-3 Season Boots
Altberg Fremington Men's 1412g RRP £174.99 (standard last with 5 width fittings)
https://www.altberg.co.uk/product/the-fremington-mens-boot-mto/Altberg Malham Men's 1344g RRP £184.99 (A-Forme last with 1 width fitting)
https://www.altberg.co.uk/product/the-malham-mens-boot-mto/3 Season Boots
Altberg Tethera Men's 1472g RRP £214.99 (standard last with 5 width fittings)
https://www.altberg.co.uk/product/the-tethera-mens-boot-mto/Altberg Nordkapp Unisex 1460g RRP £219.99 (A-Forme last with 1 width fitting)
https://www.altberg.co.uk/product/factory-stock-nordkapp/If the model of a boot made on the standard last doesn't quite fit or suit your particular foot shape and volume it's a fairly safe be that the boot made on the A-Forme last will. There are other models available for wider fitting feet.
Any of those boots listed above will be more than up to your needs but my personal choice would be the Tethera which can easily cope with all the weather conditions and terrain the UK can throw at you including winter use.
You can find your nearest stockist here
https://www.altberg.co.uk/stockists/ The ones to look for are the Premier Retailers with the red flags on the map who have been trained by Altberg staff and tend to carry a wider range of stock. NB You may need to travel quite some distance to get to your nearest Premier Retailer. Wherever you choose to go make sure you phone before you go so you don't waste time and money travelling to look at something that's not in stock.
Once you know which model boot you want and most importantly have been properly measured so you know the size and width fitting you require most of the models can be bought cheaper online than the RRP. Occasional second hand bargains also appear on eBay quite regularly.
A hell of a trek from down south but from personal experience I would highly recommend a visit to Whalley Warm & Dry
https://www.whalleyoutdoor.co.uk/boot-fitting-service/ who are an Altberg Premier Retailer and cannot recommend their boot fitting service highly enough. Customers travel from all over the country to use their boot fitting skills and services and are highly recommended by many other forum members. If you ever get up to the Lake District or Yorkshire Dales it's well worth making a detour for a boot fitting appointment.
This guide and videos may be worth a look
http://www.gooutdoors.co.uk/expert-advice/hill-walking-boots and this older Go Outdoors video is also worth watching
https://www.youtube.com/watch?v=RZ9hb65XfIs as it explains what type of boot you need to be looking for to best suit the type of walking you do.