Replace Dual Valves with TRVs ?
You are quite right to question the advice given by the British Gas Person. He sounds like a rip off merchant. I can think of no radiator which has been available in the UK in the past forty years that has been specifically made for twin entry valves having no tapping at the other end. This tapping is usually plugged with a 1/2″ BSP male plug which can be undone with a square ended key. If you find this tapping exists, it will also be a simple matter to flush out the radiator with a hose after first removing the radiator to the garden.
