You didn't bother to tell us the maker but a quick Google search suggests these are Challenger sold through Argos.
Cheapo Chinese pile ';em high & sell 'em cheap with next to no support.
If you'd bothered to do a quick search for yourself, you'd have found results like these:
http://bit.ly/20DtPDZ
espares MAY be a goo dplace to start but I wouldn't indulge in breath holding.
Anon, May 2016
