MM wrote:
Been away for a few days and the lawn is now covered in long-ish
grasses! When I go over with the hand mower, these foot-long blades of
grass are simply pushed flat, then spring up again after an hour or
so.

I'm thinking of buying a rechargeable (thus cordless) hedgetrimmer and
use it like an Allen scythe to cut these long grasses down to size.

Any other ideas? I could get down on my hands and knees with the
shears, but it would take two days to cover the whole lawn like that.

MM
I've had the same trouble myself, and the way I got over it was to make
a second cut at right angles to the first.The grass is lying down and
should enter parallel to the blade so that it is cut off nearer the
root.(I take it you are using a cylinder mower).You may need to go over
it a third time on the first occasion, but once you have got rid of the
long blades of grass it should be plain sailing thereafter. Good Luck.