I'm from near Southport originally but I live here now.
This is my build. The bricks are just standard pressed bricks fired at 1100-1300C and are standing the use no problem. Mortar is a mix of lime, fireclay and cement. It is a half-barrel design but I eliminated the chimney arch by using two pieces of 1" steel angle instead, and that works fine.
I've been running my oven for about six months and have come to an understanding with it. The 'cruising temperature' is 340C, it doesn't use much fuel to keep it there. I have had it overscale a few times, the front thermometer tops out at 500C and the gun at 550C and it was rather past that... I'm an engineer and I am considering a new design. For me, the traditional design has certain problems that I don't like.