I have a camping gaz bottle that holds six pounds of butane and it is
coloured blue.

Recently, my wife bought herself a new double burner and grill unit
which came with a regulator and pipe. The regulator, which is flattish
and about 2 to 3 inches in diam. and is marked up 28. This looks like
being a diaphragm type letting out gas at 28mB.

The bottle was originally bought for a double burner and grill about 40
years ago (tilly titan IIRC)and the regulator we used on it is about an
inch tall, disregarding the threaded parts and about 7/8 of an inch in
diam.
I have just tried blowing through it after opening the valve and there
is very little resistance.Does anyone know at what pressure the gas
comes out it?

Dave