Pizza crust lack of flavor
Looking at King Arthur Flour's website it appears that both their Sir Lancelot flour, and their bread flour have Malted Barley flour added, which is likely the source of that extra flavour you experience.

As far as I am aware this isn't a style of flour we much have in the UK, anything here which is headlined as 'malted' will be more like what you may be familiar with as a sprouted grain flour, I believe.

Your best bet may be to import Sir Lancelot for yourselves or to look for 'Diastic Malt Flour' or 'Diastic Malt Powder' and experiment with adding that to see if you can hit the right result.

That said, most supermarket bread flours are not as strong as Sir Lancelot eg Sainsbury's is 13.6% protein to SL's 14.2%. I understand that this is just a product of the fact that the UK climate just doesn't grow such hard wheats as the Americas. The flour I use for sourdough bread and pizzas is Marriage's Very Strong Canadian at 14.9%