I mostly share your view on the rights of store staff on shoplifters, but I would say a rugby tackle is a bit risky due to the chance of them banging their head etc etc.http://www.e-lawresources.co.uk/S-47-Actual-Bodily-Harm-(ABH).php might help.
Or: http://londoncriminalsolicitors.co.uk/violent-crimes/actual-bodily-harm-abh/
which seems to make clear it was not ABH in your case.
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FWIW, personally I do believe a store security guard should be able to use reasonable force to apprehend someone he reasonably believes to be engaging in theft from the store (which as you removed an item without permission with the intent to permanently deprive, I believe you technically were committing it even if in likelihood a case would not have succeeded). Otherwise that is giving carte blanche to theft. To me it would be reasonable to use something like a rugby tackle, but not to fire a weapon nor to use any more force than required for restraint once caught.
Please could you quote the relevant sections from your links? I have poor signal atm.