None co-operation during merging

[Bennet]

I seem to have this odd issue when trying to merge at low speeds (20 to 30 mph) where the driver I'm attempting to merge in front of isn't making a bid for the lead, but nor are they co-operating by dropping back. Instead they just hover around my rear quarter, maintaining pace, up to and beyond the point where there is comfortably room for two cars to travel side by side as the road narrows to a single lane.

On several occasions this has led to me slowing to a complete stop in order to avoid colliding with them. Cue horns and gesturing from everyone around, including the car (to my mind) causing the problem.

This isn't a car I've just overtaken either. I'll have had the clear lead the entire time. I could accelerate but I'm trying to maintain a safety gap between myself and the car in front and I don't especially feel that I should be chased through the merge.

Does anyone else find themselves in this situation? I'm coming across it at least a couple of times per month. Any strategies for dealing with it?