A Moorhen, or to give it its Sunday name, Gallinul Chlorapus.
My RSPB book says their habitat is around freshwater lakes, rivers, ditches and small ponds; also found in parks.
Bizarrely, we don't have a garden pond and we're some way away from standing water (though we have a medieval pond next to our front lawn, heavily overgrown and stagnant so don't think they're from there. (we're also 25.6 miles from the Lincolnshire coast) yet we've had a pair of Moorhen's visiting the garden for the last month or so. Yesterday I wasn't quick enough to capture one of them in the bird bath splashing around, so was pleased to watch one of them pop up today to drink and get in it.
That's amazing and a great photo. I used to have a pair of Mallard ducks visiting my garden a few years ago. They used to walk along the path from the river which is about a mile away. I then started feeding them duck food so I was sad when they didn't come again.
Nice capture!