North London Beekeeper so we are in the same micro climate. if you go with nationals then you will find the larger national 14x12 brood box better in london
Especaily as any london Drone bee that willl mate with your queen will give her off sping a high % of Italain or Carnolian mongrel's DNA
Or if you start with a Nuc in a national standard brood you can extend later with 14x12 Eke ( £17 from Thornes) so you can take the deeper 14x12 frames when your bees get too large for a standard
There is a beekeeping suplliers in blackheath who is quite user freindly and stocks thornes items or you will find others on here who make and sell hives, i think Hivemaker, Admin do and also Tom Bick in Hounslow ( Tom Bick does a pitched roof for a national that make a national look more like her indoors thinks a beehive (WBC type) should look like)
Thornes sale is also now on, and they do second quality hives ,which may also suit you.
And london season starts earlier and ends later and has warmer winters, so a lot of what is in the book is out of step with london Bees..and the Bees dont read anyway