Yep, B&Q etc.... assuming they have the correct diameter. If not, a bit of sneaky self-help.
Clean off the end of your pole, dry etc... stick some sticky labels, tape on the end, just a thin single layer. Cover this in vaseline. Get some fine glass fibre mesh from a car accesory shop, and some glass fibre resin. Wrap the glass fibre mesh around the pole (where you have taped it), then paint the mesh with resin/hardener. When you have finised & this is set, you can pull the resulting tube from your pole, remove the tape, and you will find the pole will be a nice fit into the tube.
Dig hole in garden, concrete the tube in...vertical, please.... job done.

