Although there appears to be a 2 to 4 week delivery estimate at the moment, this is the cheapest I can find them for at the moment (although if anyone can find them cheaper I'll cancel my amazon order :) ):
NOTE: the default seller seems to be Pharmacy Place at £15.90 so remember to select Amazon.co.uk as the seller to get them at £10.43.
Pack of 4 replacement toothbrush heads with a flossing action
Micropulse bristles grip the surface of the teeth to sweep away food and plaque
Delivers a clinically superior clean vs. Oral-B Precision Clean
Surrounds each tooth for superior and thorough cleaning
Suitable for all Braun Oral-B rechargeable toothbrushes except Sonic