I'd suggest you take a look at The Pond Forum.
There are members there from the UK as well as the US. What you can stock in a pond in the UK depends on where you are located there, and your yearly climate, as well as how deep your pond is, where it's sited on your land, etc.
And yes, the same fish who need dechlorinated water in aquaria also need it in a pond - so no, just using the water from a garden hose to fill and plop fish into will not work. Some people are able to top off large ponds with the garden hose with no dechlor, because the amount used to top off is so minor in comparison to overall pond volume.