Wilko "go with the flow" Sink & Drain unblocker kit 500ml & tool INSTORE £1@ Wilkinson's
Can't see this online but have bought it in 2 stores. Comes with 500ml of easy pour gel and a plastic crud puller.
About a quarter of the big brand products and works very well IMO especially if you leave overnight.
Have paid a LOT more for specialist products and this does exactly the same job. I know caustic soda is meant to be good but never seems to dissolve well for me maybe doing something wrong!?
But then you need a receptacle and stirrer - this is a lot easier
Found with all the similar branded products in a white box