Rich,as a rule of thumb, the water should be circulated once or twice an hour through the filtering material(s). Taking into account the friction loss due to bends, fittings etc in the plumbing,I would suggest that you would require a pumping capacity of at least 6000 Liters per hour for your pond.

It is usual to have both mechanical and biological filtration. Though it is only right to point out that there are some pond owners, who do not employ any filtration for their ponds.
Personally, I would advise the use of filtration in a garden pond. Especially when you intend to have fish.

Mechanical filtration would be required, in the form of a pre-filter screen before the pump's intake, to trap any large debris that could plug the pump or damage the pump's impeller.

Biological filtration is employed to condition the water and treat it for ammonia, nitrates that a result of fish and plant wastes. Biological filters are usually located outside of the pond and the water is pumped through them and back into the pond.
Various companies manufacture in pond combination mechanical/bio-filters but they are usually quite small and plug up quickly.
My personal suggestion is that you build your own bio-filter for outside of the pond.
Google for ideas.
As your pond ages the growth on the sides and bottom of your pond will eventually become part of the biological filtration process.

I have never had the need for a UV light but their are lots of people who use them to control green water(algae blooms).

"Horton"

P.S. there is a UK Pond forum here at GW. Though not used as much as it used to be, you may find information there, about pond products etc, that is more pertinent to your area.

Here is a link that might be useful: UK pond forum.

Thanks Horton

I may have over sized the pond. i think its more like a 5000ltrs.
but what ever size you reacon 1 to 2 times an hour, thats great.
I will find a suitable pump and match the filter to that. probebly a black box with UV or a green ginie UV.