Reply to Gill B, Claire and Helen
Bumblebees are relatively docile compared to honeybees and wasps, so you could tolerate them until the nests finish in autumn. After the queens and new males (drones) are produced, the nest winds down and eventually is abandoned. This is the time to clear it out. The only bees about in winter are mated queens which leave to find a warm dry place in hedge bottoms, disused mouse nests and other secret places to hibernate. They will not seek out the old nest to reuse it, but because it as in a suitable place this year, the same site may be found by next year's founder queens, so clearance/disturbance this winter may prevent occupancy next year.