2 gang 2 way switch with only one common terminal

[Itisonlyme]

Thanks for the advice, I am thinking this is way past my level of competence and needs a professional. As I also want the CU changed and juice run out to the summerhouse there seems little point me mucking about with this as it is clearly not a straight swap out of the original fitting I had hoped for.

 

[Itisonlyme]

Update on this is that the dimmer has gone faulty anyway and I replaced with what would have been a like for like replacement two gang two way switch and rewired back to the original circuit. Simples!

Spec on the dimmers said a minimum load of 60 watt which may be the cause of the fault as I was loading below that.

Many thanks to all who offered advice.