Bought shaving supplies, like Personna Injector Blades, from Connaught Shaving too, even though I live in Singapore. Not sure if they're the cheapest option in the UK though.
If your concern has to do with counterfeits, I bought blades sold and shipped by Amazon and never had a problem.
Oftentimes they have better prices than specialist stores: last Feathers I bought were ~33 Eurocents a piece, elsewhere a comparable amount of blades would come down to about 0.45 Euros each.