Thought I’d answer my own question having found the fix.
The problem is the seals on the condenser had worn and needed replacement. You can still order these direct from Miele and cost around £25 each. The condenser tunnel should remain dry and with worn seals the water at the back can leak back into the tunnel and be blown over the edge as described.
Some people are selling a complete condenser unit for around £260 but you only need the seals assuming your original is intact.
The Miele parts catalogue can be accessed here (Miele parts catalogue) and simply enter your model number.
If you’ve taken the back metal plate off you’ll need to remove the old seal and refit using RTV available from any good car parts store. RTV is used to seal oil sumps, head gaskets and similar and generally works to temperatures over 200 degrees celsius.
Hope this helps anyone that has a similar problem.