I am trying to install a 2 gang, 1way dimmer switch in my living room. On my new switch are 2 sets of L1, L2 and ~ with an arrow through. Coming out of the wall are 3 sets of grey wires each containing 1 brown 1blue and an earth.? Please can anyone advise me what to do?

Chris, where are you located?

Obviously you are outside the US so I will not give you any other advice than to hook up the dimmers the same way the old switches were.