I don't know what materials are available in the U.K., but if I were to make one here in the U.S., I believe I would use PVC or ABS pipe for the pole. If one pole isn't long enough, I would join more lengths with in-line connectors. I would anchor it in concrete blocks. (Thrust the pole through the openings in a number of blocks, then pour in pea-size gravel to prevent tipping.) I would paint the pole to make it prettier, and I would hide the blocks with fabric.

Before erecting the pole, fasten the ribbons to the top.

This method uses cheap materials which are readily available and could be used for something else once the celebration is over.