*Sigh* Two in as many years says something about this components "quality". Sure you don't need a new impeller/impeller shaft too, if the split is allowing the impeller shaft to move while the impeller spins, the impeller or shaft may get damage9 as a result, as it is spinning round 50 times a second after all...
I'd be tempted to super-glue the outside of the crack (i.e. the media side) rather than replace it... But hey, that's just me. £6.50 is likely to be very cheap for a replacement, but Google Product Search may find one cheaper (but ask it to order by price, low to high, or you'll be looking though all day no doubt...)
All the best
Rabbut