Speaking with my other hat on as a private landlord ...
... claim that there wasn't a need for an RCD board ...
That is actually correct.
For a
new installation or additions then RCD protection is required for some circuits (sockets in particular). However they isn't, and never had been, any requirement to retrospectively apply new regs to existing installations. The other defects (related to bonding I believe) could have been met without replacing the consumer unit - but it's often easier to replace the CU and remove some of the bonding requirements.
This is a tricky area, judging how far anyone should be "forced" to go in terms of updating an existing installation. There's an element here of "backside covering", in that while there is no requirement to upgrade existing installations, there then comes the argument (potentially if something happens, or I get a "b***ard tenant"*) of arguing whether something that met previous regs but doesn't meet current regs is "reasonably safe" which is what the law requires. The decision I took 3 years ago (when I added a second property and the first was empty) was to upgrade - by careful equipment selection and doing most of the work myself I was able to keep the costs very reasonable.
Also, is it reasonable to expect significantly higher standards in a rented property compared to one you own ? I'm not aware of many (well in fact, any) people who have made a decision along the lines of "ooh, the regs have changed, I'm going to update my electrics" without there being some other reason to do so.
I do have to say though that your landlord is not very reasonable. Actually I'd go further and say he's the sort that saddles the responsible ones of us with unnecessary red tape. If you have evidence that he provided untrue gas safety certificates in the past then please, please report him to the Gas Safe Register. There is no room for cowboys like that and they need weeding out - he gets no sympathy from me.
I also find the response you got from the council officer "rather disturbing". It's an implied term (ie one that's implied into any tenancy by law and cannot be contracted out of) that a rented dwelling should be habitable - and that includes having working fresh water and sanitation. These days, not having running hot water wouldn't normally be counted as having adequate sanitation facilities. I think you should be having words with the council again, and potentially make a complaint.
I admit I do find myself in a bit of a "do you, don't you ?" situation here. As a landlord I'm not generally in favour of getting councils to stick their noses in and have the opportunity to cause hassle. But, I also don't like seeing bad landlords give the rest of us a bad name, so I support measures that persuade them to improve their game. In your case, I think the latter applies.
* I've only had one, but that was one too many. Remember that there are two sides to every story - in a property with no prior or post problems with damp and/or mould, one tenant managed to make every single surface in the flat grow mould - and then complained to the council before mentioning it to me. I'm fairly certain they were hoping the council would "suggest" that the rent was too high for a damp and mouldy flat. On top of that, I had complaints from almost all the neighbours, and they scammed an insurance claim off one of them for alleged damage to their van.
By the time I'd got the place fully back into the standard I expect of something I let, I reckon it cost me several months worth of rent.