Id say, in this situation, the main switch of the DB Could be your isolation point, and this can almost always be locked off if you have the correct bit of kit. 

C3 - local isolation would be better.

IMO of course. 

Cheers Tatty, the CU has an up front RCD built into the board and it turns to reset rather than an up and down toggle switch so can't be locked off, the mcbs dont have a hole in either to fit a lock . I think a C3 is probably right just thought i would see if i was missing anything. I personally don't like shower switches, whenever there is a problem it is nearly always the isolation switch. That said i have never been able to not fit one.

I might be tempted with a double rcbo though on something newer. I was looking through isolation and switching in my regs book, it says lots of things that the isolators should do or where they should be positioned if they are fitted  etc  but doesn't specifically say they should be fitted. As i said in OP it does not appear to be a manufacturers requirement either just a recommendation.

Gary

the mcbs dont have a hole in either to fit a lock

Some MCBs were designed to use a lock-off that clamped straight onto the toggles - no holes needed. e.g. https://martindale-electric.co.uk/product/martindale-lok8-compact-mcb-lock-off-device/

   - Andy.

the mcbs dont have a hole in either to fit a lock

Some MCBs were designed to use a lock-off that clamped straight onto the toggles - no holes needed. e.g. https://martindale-electric.co.uk/product/martindale-lok8-compact-mcb-lock-off-device/

   - Andy.

Well, they are 3 parts useless, but they will get you through a C&G assessment. I think that the point of locking off is not absolutely to ensure that a switch cannot be moved (same as a padlock on a door can always be removed if you try hard enough), but that such an action must be deliberate.

Assuming that the shower has its own circuit, it seems a bit odd not to have some form of functional isolation (even if it is just in the line) but I do not think that in itself gives rise to a C3. Nor do I think that the difficulty of locking off does so - you would have to give a C3 for all of the circuits.

I see your point about all the circuits. The more i think about it i am comfortable with a C3. The problem i see is if a plumber comes to change the shower he has no control of the CU and no local isolator.

I appreciate the input. Thanks guys

Gary