Ken Ellis wrote:
I have a reasonable quality lawn with no ryegrass in it. I want to buy about
a kilo of seed, with a high proportion of browntop, for overseeding.

Most bowling greens use a mixture of about 20% fescues and 80%
browntop, so it might be worth seeking out the groundsman at your local
bowling club. I bet he'd swap half a kilo of seed for, say, 4 pints of
spitfire ale.