Thanks for all the help.
The circuit does have a double pole isolator switch, in fact the whole installation is only a couple of years old. The Triton shower "boiler" and PRD have both failed an the spare parts were considerably more than a replacement shower.
Many thanks for your replies.
My fault I should have made my explanation more clear. The shower is 8.5KW and is cabled in 6mm with a 40amp MCB. The existing cable is routed in trunking with a cable run of about 8m.
The existing cable is long enough to enter the shower housing but is...
I need to replace my instant electric shower. However, the new shower I have bought has the cable entry points on the Opposite side to the old unit and I need to extend the supply by approximately 300mm. Can anybody advise me on if this is acceptable under part P and if jointing is ok what if...