I've just thought to give you some update. Today the pipe arrived from Germany, I managed to replace the broken one so it is okay now. WD40 did the job on the rusty screw-nuts and it was not complicated to change the pipe.
I did not find car part shop in the UK selling stuff for LHDs, so I used this company: http://www.axel-augustin.de/
They dispatch within a day and shipping takes 3-5 days.
The other company in Poland ( http://shop.etscompany.eu/
) would have been cheaper but dispatching takes longer, therefore I chose the other one.