@Lee (slightly off-tack, but...)
<<You appear to then be inferring we are a bit thick for assuming a non-uniform copper cannot make an arrest>>
Stop-and-seach isn't an arrest.* Therein lies the problem. stop 'n' search needs uniform, else it'd be easy to use that excuse for a series of muggings. However, a non-unifirmed copper _can_ make an arrest. I learnt that years ago from the Sweeny. Plus, from my Panda (union) Police pocket book, which stated:-
"A Constable is a citizen, locally appointed but having authority under the Crown for the protection of life and property, the prevention and detection of crime, the maintenance of order and the prosecution of offenders against the peace".
I learned that by heart, 35 years ago, as a trainee bobbie when even our whistles were inspected for being polished (Noo, Finbarr, Nooo!!!). Never forgotten it, BUT it puts the emphasis on Citizen, not uniform.
I believe, unless the law has changed, that anyone can make a citizens arrest, within guidelines - mainly common sense. It's stronger here in Finland, where it's illegal to ignore a threat, if you can reasonably deal with it. For example, driving, spot a fallen tree branch in the road, you absolutely MUST stop and move it if able. If not physically able, ensure the authorities are there before you leave. Another: See a drunk lying in the snow, you absolutely must offer assistance (even just call the cops) - it's not an option. You can't walk by. Nick his wallet first, natch. "Services Rendered".
(Still waiting delivery of the Feisty wife, Lee. Sadly no photos - Kodak don't make Kodachrome any more, and I never did get the hang of these digi - diga - battery operated pinhole cameras).
*From the Home Office site "if you’re carrying something illegal, such as a weapon, or the police believe you’ve committed a crime, you may be arrested". So, if you _may_ be arrested, then you haven't already been.
Site at http://www.homeoffice.gov.uk/police/powers/stop-and-search/