Thanks for the replies.
PeterW: I would be putting a perforated pipe wrapped in geotex and 20mm gravel behind the wall - it will be 150mm wide at most and can sit on top of your founds if needed.
I already have about 2 metres of wall built last summer before any water flow started. I obviously do not have 150mm pipe behind that.
PeterW: Concrete will art under water - if it is readymix then it will just displace the water, you could always ask for a rapid mix. I would also use shuttering your lift the level of the foundation edges slightly.
Not sure what concrete will 'art' means. I will definitely use rapid mix as you suggest.
Are you saying the shuttering should be above the foundations, or I raise the foundations. Surely, all this will do is is get the water flowing over the shuttering while building or over the foundation when that is laid?
PeterW: Need to see a photo if possible.
I cannot provide a photo as I do not have a modern digital camera. Sorry about that, but I do not really want a smart phone in my life.
Jeremy: The normal solution for both is to install a land drain in a gravel bed at the retained side of the wall, as @PeterW suggests above. We had to do this behind our big retaining wall, as a requirement stipulated by the SE that designed it.
I cannot do anything behind the wall on the vertical mud of my neighbour's property. It is not my land. I have very limited space in front up to my house, it is less than a metre.
The old, thin, 1 metre tall wall never failed before, but there was never any water before. The water is something new. It has never happened in over ten years, even when there was a gap between the old and new wall when we were building the wall in stages.
Jeremy: How high is the wall?
The wall will be up to 6 ft to cover the retained mud and a bit more, also for privacy. However, I can limit it 1 metre and put a fence on top if necessary.
Declan: Dig a hole to act like a sump and guide the water into the hole. Then you can either pump it out to a drain or bucket it depending on the flow.
I have presently built a temporary sump. I direct the water to the sump which then auto-pumps it away with a pump I have bought.
However, you still get this constant 1cm to 2cm deep flow right at the point where I need to put the next breeze block.
Me: I can put loads of weep holes in the 2 metre stretch I have already built. And putting weep holes into the new bit I will build will be easy. I can then have a sort of French-Drain to divert the water on my side of the property to a permanent sump I will build.
Will that be OK? I have to work with what I have.