Removing Rear Lamp Cluster

I would appreciate any tips on the best way to remove the rear lamp cluster on an 06 Mk2 5 door Focus (UK model).
It is held on the inner side by two screws. The owner's handbook (page
187) says remove the screws then gently pull out the light housing. I have tried the gentle approach and it doesn't work. From the line drawing in the handbook there appear to be 2 (or maybe 3) retaining clips moulded into the plastic housing under the outer side. I am reluctant to use too much force in case I break them.
Any advice will be much appreciated.
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