Nope, he asked what type... anyways. To take them in order (note in all of this there will be differences of opinion)
Single RCD does not comply with wiring regulations. Not something to do as you have a single point of failure.
Dual RCD also has a single failure point for half of the house. Although this is a common arrangement, it doesn't acually meet the reg requirement of separation of circuits.
RCBO is the way to go, RCBO prices are reducing and is the way to go.
Well, as the man with a wooden leg said, its a matter of opinion. For a domestic premises you need to consider what you have in your house and if you have stuff that needs protection. Best to read this guidance from NICEIC
18th Edition requirements Regulation 443.4 requires that protection against transient overvoltages is provided where such overvoltage occurrences could result in: • serious injury to, or loss of, human life, • interruption of public services, • damage to cultural heritage, • interruption of commercial or industrial activity, or • where a large number of individuals at the same location could be affected. This regulation also states that in all other cases a risk assessment according to Regulation 443.5 should be performed in order to determine if protection against transient overvoltage is required. If such a risk assessment is not performed, the electrical installation should be provided with protection against transient overvoltage.
Have your electrician carry out the risk assessment, then he can decide. He/she will have to sign the certificate that includes the risk assessment.
The DNO is not involved, but the local authority is. In Scotland I believe that you need a competent installer - SELECT or NICEIC member. There are options for an Unregistered Installer, but that will require testing by a qualified electrician.
I'm not familiar with certification procedures in the frozen North. This may help
https://www.inverclyde.gov.uk/assets/attach/516/GuidanceNote3-ElectricalGuidance-Web.pdf
Ahh. Can of Worms time. When I started the two 100% solid UK manufacturers of CUs were MK and Wylex.
In 2019, MK (then owned by Honeywell) announced that they were ceasing production of CUs. There had been many moans about decreasing product quality after manufacturing moved to the far East. Another company - CircPro - acquired the licence to continue manufacture. But I havent touched MK since.
The other long-term reliable company, Wylex, was acquired by Electrium. About ten years ago, some Wylex MCBs started failing (see pic below!) and a huge recall process was launched......
So, its a lottery. For the last several years I have set on Hager. Not the cheapest, but very reliable and most of the new kit fits (and look like) the old kit.
There are new entrants to the market. I hear good reports about Fusebox. I've never trusted cheapo budget brands for anything.......
Again, trust your local friendly electrician.
Thats about all I can do for now....