Adding a 2 way unit to a garage

[Mfctitch]

Evening everyone

I have been asked to price to add some more sockets and lights to a garage plus a few out side sockets.
now the garage already had a supply from the house via SWA cabling which just feeds a socket and the lights via a fused switched spur.
now the consumer unit in the house is an old "Ashley & Rock" with Supasafe MCB's. with blue writing if that helps the whole lot is protected with one main RCD.

Now for my question.
I know that I can fit just a 2 way unit but I was thinking that with more sockets and some of them outside it would be better to fit an RCD in the garage.
but I need this to trip before the house RCD trips so any suggestions would be great.

Thanks for all suggestions

 

[kingeri]

As a spark, there are times when a customer will not pay for a job doing the proper way. They think you can just bang sockets in etc and cannot see why you need to make changes at the CU. Yes, the job may end up being done by a cowboy, but that's not your problem, you have to learn that sometimes you must walk away. It can be frustrating, but if you work out what needs doing, how much it will cost,and the customer is unwilling to pay, what else can you do?