Here is the outcome of the £20 repair rather than £200+ replacement.
The original flexi pipe was welded to the little silencer box but was relatively easily removed and what little remains of the weld can be filed off the silencer inlet pipe leaving a smooth mating surface for the new pipe. I used the same type of stainless steel Eberpascher clamp to attach the pipe to the silencer that is used at the other end to make the joint to the heater unit.... problem solved.
Martin
Congratulations on the fix! Nice photo