Mike Lyle wrote:
That will _sometimes_ work, especially if you use clean hard-core
rather than gravel, and incorporate a lot of loose stuff into the
topsoil. But the holes will have to be big ones. If your lawn just
gets a bit "noisy" and squelchy after rain, that could be enough; but
if you can actually see water half an hour after the rain has
stopped, then I'd say it won't.

You really should chat to your neighbours about it: either they have
the same problem, and can tell you what they did about it, or your
garden is the lucky recipient of all the water from their gardens!

Sounds like a case for a paved area to me: keep it clear of the
damp-proof course.

--
Mike.

Even a thin layer of sand/topsoil mix on my garden was enough to stop
the top level squelchyness as the sand helps the water disperse rather
than sit in a puddle. The OP said the garden slopes and I guess it's
just the lower part of the garden that gets waterlogged?