You should really be asking us this question with a description of your feet in terms of both size and width. As any decent boot fitters will tell you, not all boots fit all feet. Also remember that the lasting can change when the boots are updated and last year's fit may be different to this year's model (Salomon please note).
A couple of tips: if you go for a fitting, go in the afternoon, preferably after a decent walk, so your feet will be at their maximum size and width for the day and take your own clean "worn-in" hiking socks that you will be wearing with them (and any custom insoles if you use them). If you find the staff unknowledgeable, try asking the store manager for help. If you are trying the mail order route, when you get your boots delivered, take out the insoles and put your feet on them, stand up and assess the fit between the new boots and your existing ones. Try it again when you wake up and at the end of the day and see how much your feet change in size/shape. Wear a pair for at last an hour including doing lots of stairs. You need to see about 1cm gap at the front. If you get heel-lift, try different lacing methods to set the correct width for your forefoot and then lock the laces firmly at the ankle using surgeons knots (one extra turn) to hold the tongue centrally. For me, any remaining heel-lift is a no-no for purchase.
I have size 12.5 narrow feet with one normal arch and one high arch and wear custom insoles (brilliant). Usually size 48's will fit me but not in all brands. I have had several pairs of Zamberlan 996 Vioz GTX boots over the years which have an excellent build quality and fit. I and several friends have various Altbergs - not the most fashionable perhaps, but well made and available in a range of widths. I have also been wearing Scarpa boots for decades as they fit my feet and currently a pair of two-year old Marmolada Treks (not the stiffer Pro version) and 4 year-old Charmoz winter boots which have been excellent. Scarpa also have a trustworthy and responsive product return service should you need it.
If you are still unsure and it is a hell of a long journey from Watford, but has the advantage that you can walk in the Lakes for the weekend: visit George Fisher in Keswick. Great range of boots stocked, with expert boot fitters and as far as I am aware, the only shop I have heard of where once you have worn you have worn the boots on the hill a few times, they will still take the boots back if you cannot get on with them, with an allowance for wear and tear. As they sell these returned boots in the shop, you can often get a bargain if you are lucky and amazingly, these are also covered by the same guarantee! They also offer an exchange on Fishers-purchased used junior boots, if your kids grow out of them. See:
https://georgefisher.co.uk/pages/visit-george-fisher-services-boot-fitting. You could also talk to them about what they could offer you as a mail order customer - I don't know if they do virtual boot fitting.
As already mentioned, Whalley Warm and Dry in Whalley also do a very professional measuring and boot fitting service, but don't offer the take-back service.