As already said, Marford short walk is the place to go if you'd like to catch 40 Barbel in a day and you don't mind getting up early, the long walk is a lot more natural and is more suited to a mobile approach, plenty of Barbel, Chub and good roach, both stretches have a night fishing restriction.
Leasey bridge is an altogether more natural fishery than the short walk, the Barbel are mostly 2-5lb, which to my mind is far more in keeping with diminutive nature of the river than the pellet fattened fish downstream at Marford. It also has the backwater, this is a pond/lake connected to the river, it, and the river, have never been stocked and it holds lots of Tench, mostly small but has produced 5lbers, some very good roach, lots of small Rudd and Perch and quite a few Barbel. The Barbel tend to be bigger than in the river, averaging 6 1/2-7lb, a fair few Carp have taken up residence too, together with Chub.
Fishing at Leasey is up to midnight summer and winter and night fishing is very popular.
The Ouse fisheries are fabulous but have suffered the well known problems all the Ouse has lately, the silverfish seem to be making a comeback though to fill the gap.
The Lea fisheries are a great antidote to a few blanks up on the Ouse.
Last year I fished the Ivel for the first time, what a lovely and interesting bit of water, not caught anything exceptional yet but roll on next year! It's been severely Ottered Barbelwise but lots of good Roach and Chub to have a go at. There are still some big Barbel there but 'the big one' was an otters lunch one day so the bivvy circus has moved on and it's not quite as manic as it was.
Verulam is a brilliant club, you'd not regret joining I'm sure.