There was a recent thread recently Razor blades and I posted the Wilko do some which are compatible with Gillette.
We happened to visit Wilko today, they seem only do the triple version now although they still fit the Contour / Sensor handle which used to use twin blades. £3.20 for 5.
I’ve used them before, they are sharp and seem to last. In particular the lub strip seems to last longer than the Gillette one did.