With luck you have bought Callistemon citrinus 'Splendens', since
there is no splendens as a straight species

Yes, that's the one. It was an impulse purchase at the garden centre -
they had a large display specimen in flower and I thought "I gotta get
me one of those!" =;-)

After planting, Callistemons can be a bit late to commence growing
following the first winter - especially young plants that have been
tunnel-grown in the nursery

I don't know how old it was when we bought it, but we had snow last
winter (we live in Essex, and snow is a rarity) and the tips of the
stems seemed to suffer. I removed the frost-damaged parts and it came
back strongly - plenty of green bushy growth, but no evidence of large
flower buds. Given what you said, the frost probably did for the
flowers for this year

Many thanks for the other advice!

GR