Over the last 3 or 4 years I've become a fan of Cerafix Grabs Like
Nails. It is now off the shelves at B&Q.

Its replacement at B&Q is B&Q Exterior Grab Adhesive, which IMHE after
trialling it, isn't a patch on Grabs.

Puzzled enquiries yielded:

Cerafix is a B&Q own label brand, as was Grabs Like Nails.

Maker of Grabs was Henkel which still makes several other Cerafix
products for B&Q. B&Q wanted to pay a lower price to Henkel for Grabs.
Henkel w/couldn't play ball, so B&Q chose a lower spec from xyz plc.

Henkel suggest their Unibond Megagrip adhesive as substitute for Grabs.
Stated availability is builders merchants such as Jewsons, Travis
Perkins.