bash: please provide an easy way to spawn a new process group from script

[clime]

I was battling this problem now for several hours

i wanted to do this:

{ a | b; } & pid=$!

and then later

kill -- -$pid

to kill all the processes spawned by the pipeline.

But this proved to be immensely complicated as no new process group is
spawned from within a script (unless set -m which is not recommended
as it blocks signals)

Please, provide a syntactic construct to spawn a new process group (or
at least there should be some usable command to do that).

Thank you
clime