Further to my previous answer, If you go to the Screwfix website and search for item 6854R it should bring up the part you need for less than 2 quid.
Rupert
March 2019
The best solution would be to swap the part for a longer version. If you can find a local plumbers merchants they will have what you need as this is a very common replacement part and easily available.
Rupert
March 2019
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