We've got a raised bed at the end of the patio and have recently noticed a
hole/tunnel/burrow at one end.

Neatly dug, about 3" diameter. We assumed it was rats and have put down
three lots of poison, which disappeared and we closed the hole.

A few weeks later another one has appeared in a different place. Never seen
anything moving day or night.

Is this likely to be rats or something else - and how do we get rid of the
little perishers?

Dave