Marq writes:

Thanks for reading.

Just bought some Growmore and it says on the box to "fork in well" to
prepare a veg plot.

I admit I'm not the sharpest, but does that mean the full depth of a fork
or just a couple of inches?

"Yes"

Think of where the roots of whatever you're planting in a particular
spot will be, fertiliser needs to be distributed between the top of
the soil and there so the plants can feed continuously while they are
growing. Top dressing will wash through to a greater or lesser extent,
but judging how long it will take is very dependent on your soil and
how much rain happens. If it doesn't percolate down the surface roots
of the plants will develop more than the deep ones and the crops will
be prone to drying out.

Anthony