Yes there are instruments available to measure the door closing force. usually in automatic doors with electronic control with VVVF or a DC motor electronics is available to adjust the closing force.

Am not aware of the UK standard but know the possibility of adjusting th closing force. It also helps in deciding the door reopen when there is an obstruction in the car or landing sill.

Usually in the Electronics the current driven by the motor is monitored and the closing force is measured

Yes it's 150newtons