In addition to the two answers citing the Highway Code - the key words are 'perfectly entitled'. The answer is 'No'. The HC does not have the force of Law in the UK, but infractions of the Code will be taken into account if a driver's actions result in an accident or an intervention by the Police.
Drivers have a duty of care to other road users, and overtaking without leaving sufficient clearance puts other road users (in this case - you) in danger. It's worth noting that a number of the cycle fatalities on London's roads over the past few years have occurred at junctions where the cyclist was attempting a left turn and was 'overtaken' by another vehicle.
The solution for the cyclist is to move to a 'control' position in the centre of the lane about 5 to 10 metres out from the junction, thus forcing following vehicles to remain behind. Do not wait at the kerb edge or creep up on the inside of waiting traffic. This is why many junctions have marked cycle space in front of the lane. You maintain the 'control' position all the way around the turn, returning to a normal riding position of around a metre out from the Kerb when it is safe to do so.
The 'control' position is taught by Bikeability instructors as part of the Government recognised cycle instruction programme offered in UK schools. It's not just for kids, it works, use it.