volvo 50 t5 - looks like starter motor is on its way out = turn ignition, light dims indicating current flowing to solenoid (and possibly the motor) but no sound or turning from the motor. (AA man connectedbattery and it started - battery is charged and less than 1 year old - AA man reckons the extra oomph overcame the resistance in the motor)

how difficult is it to whip out the starter motor - it is at the front of the engine but it is pretty crowded in the engine bay - can it it be removed from the top?

it could be the ignition siwtch or solenoid

Sounds much more like either a bad connection or a dead cell in the battery.
Clean the battery connection and main earth lead connection.
Don't assume a year old battery can't be faulty.
A dead cell in the battery is checked by measuring the battery voltage under very heavy load, if the AA man didn't do this take anything he said with a pinch of salt.