Cooker and shower on the same circuit

Well looking a that JB and the CU, what happens next all rather depends on the reason for the call-out. Clearly bears the hallmarks of  the first calibre work of Speedy Bodgitt and Scarper Ltd, but the cable looks in good nick - so if it has been like that for years and that is not the reason you are there, then it is slightly less urgent than if you are called out because there is smoke pouring from the switchgear or folk are reporting it tripping.

Now you are there to replace the shower - but even if the previous one was the same wattage as the new one, I'd be saying 'aha this is more complex than a direct swap'

I'd like to think very few would argue against splitting it into two circuits as the best technical solution - clearly it is.
But given what is already there,  the first act is to fix the problem called out for, only then to improve beyond. This should also involve a conversation with the customer. Do they actually use intend to use both? Maybe leaving it "as is" for now is an option, but in your shoes I'd be wary. Also depends what space is in the box for another MCB, if none then maybe it cannot be split there and then, as that would be a CU change and a world of pain.  If it really cannot be split at the board then a fatter cable from the point of split to the MCB may be nice - but nicer still if the split involved 2 MCB or fuses or one of those mini CUs with an RCD.

Some things you see do leave you wondering at how other folk decide how to solve a problem,  it reminds me of a shower I found once that had been dobbed into the CU at the main tails, bypassing all fuses and breakers completely.

As per my first post in this thread 'possible to  do' does not equate to 'it is a good idea'

Mike.

The standard of the installation work is what I would generally from someone who would dog a shower circuit into a cooker circuit or vice versa.

As you probably guessed I went for option 3 and separated the circuits, extending the shower circuit using a 63 amp junction box to make a secure connection to a new cable running back to a new B40 RCBO, along with general tidying up.

Not one I installed and it is not running off a shower circuit.

I have seen a few shower circuits dogged into the out going terminals of a consumer unit main switch  more worrying I have seen some dogged into the incoming terminals of the main switch in old rewirable fuse boards which have solid brass busbar connected directly into the main switch, so turning the main switch off doesn't isolate the shower circuit. 

Sparkingchip said:

so turning the main switch off doesn't isolate the shower circuit

Then it's not a main switch. 462.1.201. And by definition, such an arrangement also contravenes 462.1.

Yes, I know that’s a tight bending radius, it’s hard to do everything as you would like to.

Our street cables do not overheat around here because they are nicely cooled by the cool sea breezes. They are overheads.

Z.

No Z, I didn't say that, and just because it isn't a standard circuit configuration, it does not mean it is either wrong or unsafe. Those who cannot calculate and assess the circuit as found are exactly the ones who I was complaining about re competence. You have yet to point out a problem with the circuit as we are discussing it, except to try to use regulations whose relevance is highly suspect in this case. You have completely failed to understand the DNO arrangement and why it is perfectly safe and functions well almost all the time. The same goes for the arrangement under discussion. Yes it could trip if the cooker thermostat fails AND the shower is used for an hour. That is why the CPD is there! This is not in itself dangerous in any way. Your soap example is terrible, what is wrong with cold water to was the eyes. That is the normal emergency provision after all, for chemical showers.