Kent Mere wrote:

is it available in white ?
b&q don't have any,

Look in B&Q for Evostick Nail and Seal. This is the same (white) sealant
used on boats for keel to hull, and transducer through hull fixing. It's
also used above the waterline for any fitting that requires a screw to
penetrate the skin of the boat and for attaching things like handrails.

Don't be fooled by the relatively low price. It's one of the best
selants available on the market. And it's useful for other jobs since it
can be shaped (sanded) after it has set as well as overpainted.

Also good for use as in place of Gripfill.