Many thanks Andy, Gonna work all that out later.

One of our radiators in the bedroom is already making a 'banging' noise
so i think that may be a sign that there are too many rads on the run
already.

It terms of BTU i've worked it out (approx) to be

Rad 1 (600x1600) 6145
Rad 2 same 6145
Rad 3 same 6145
Rad 4 (500x1000) 3275

Total BTU 21,710 off one run going left now the 22mm goes into another
run (so only 1 pipe really)

I will do the sums later and work it out right.

Again thank you for all your help