Have a quick scan of this
Rob, 900 Lumen P7 LED lights (500-600 in reality) have been available for the last few years & are much now better value than the std torchs your suggesting (torches were great a few years back, I have two). You might get that torch for £6, but you still need batteries, charger and a mounting, all this adds up to the price of a complete bike light as per Monty’s link – which is putting supposedly 1000/1200 lumens (obviously this is theoretical max, but there definitely brighter than the measured/confirmed 5-600 lumen of P7 LED’s).
XM-L LED units are this years bargains lights.