My Langster is dragging awfully, is there anything to be done or do I have to replace it?

BB

i just squirt a load of duck oil into it,, if it doesnt get any better throw it in the bin and pay another £9.00 for a new one,,

or go and pay £60 odd for a white bros one as they can be rebuilt,,

Don't buy Dicta ones, they last no time. Shimano ones are way better for less than 15 quid.
If you need to clean yours soak it in diesel or something, wash and dry it and soak it in oil. EP90 is thick or use lots of m/c chain lube. It will then run silently as should any freewheel.

Lay it on its side, squirt some WD40 in, give the wheel a spin, and lean it over so the crap can come out.

Then lay it on its side again, and dribble some decent oil into it. Oil it weekly.