Christ, anything for night photography without using a flash and with a budget of £200??
Put a 1 in front of that and you could get a Cannon 5D Mk.2 with Full Frame Sensor, then splash another £450 on a 18-180 wide aperture Tamaron lens for it...
It is slightly confusing that you mention such a large zoom (and) good night photography, my experience says you can either shoot wide at night or not at all, unless you're doing long exposures, and even then without a specialist lens you're looking at not being able to push it much past 50mm, with no convertors, you just don't get enough light through smaller lenses, and any light you do get, at the cheap end of sensors (Normal CCDs that you get in low end bridges and all compacts) will burn out on any remaining light that comes through.
Personally if I was starting out I'd be looking at a lowish end Cannon 1100D or 650D, but these lack features that are helpful for railway photography (Fast continuous shoot speed, 1100D only managed 3.2fps)
http://www.jessops.com/online.store/products/80181/show.html
A basic starter on an 1100D would set you back about £370, but it can be added to with wider lenses and teleconvertors for better shots later, although on the size of sensor to get much better you need to push up to a 600D, but that's a big price jump.
Sonys tend to be twice as fast in the same price range, the a37 comes out at closer to £500, and 6.2fps, but even that is irritating when trying to get moving shots, and the Sony's data transfer speeds (from experience) is all out of ideas after about 7 seconds of trying to encode full res. Cannons on this rarely fall down, since even the 1100D uses the DGIC4 processor as it's a very new camera.
The main problem comes in that a stock 18-50mm lens simply can't cope and focus correctly on longer range shots, for example, at Piccadilly, you're lucky to get past 90 yards and keep the unit in proper focus without distortion, you need something at the 170mm mark to get decent approach shots, static is fine at 35mm, as are close ups, such as sitting near lineside for a passing unit, that brings me onto my next point;
An APS-C sensor is much better performing than a standard CCD in sports shots, if you wanted moving things and money was no object I'd be pointing you at the Cannon 7D with an 18-175mm lens and 1.4x teleconvertor, but that comes out at about 10 times your budget.
Thing brings me neatly to Bridge cameras, I'm not a fan of these for what the're used for, the're semi DSLRs with fixed lenses, and are very good for things like extreme sports at the high end bridges (~£400) tend to be very rugged in construction compared with the equivilant DSLR cameras.
And by the time you manage to find a bridge with some decent glass in it and a decent sized sensor you're pushing £350 anyway. For example the Cannon Powershots
http://www.jessops.com/online.store...ershot SX40 HS Digital Camera-82692/Show.html
But this will distort like hell and might not be what you're actually looking for in a camera.
To be honest what I'd say is either look at the high end compacts with a £200 budget, because Bridges and SLRs are out of budget for them, since a decent bridge is starting at £350 and an SLR setup would cost you £374.99 for a bundle with card and case, then another £15 in filters and £10 in odds and sods, I wouldn't go out with anything without a UV filter on, unless I was shooting at night and the F number was imperative, since it protects the lens quite nicely.
Either way, feel free to ask me or my better half some more questions (I'll pass them on).
I'll leave you with a shot that shows what happens when you get the settings right on a low to mid end DSLR running at 55mm and f/6.3 with a 1/200exp 100ISO on a Sony α290. (Stock Lens)
View attachment 11844
PS: Last thing I'll say is go into Jessops, not Jacobs, not Argos, not Currys, PC World, Comet, Asda, anyone like that; Jessops, and have a feel around the Bridges and lower DSLRs and see if you like the feel of them, if I was starting out in railway photography I'd either be looking at a Sony Alpha 37 or Cannon 1100D, probably the latter due to the improved lens offerings from Tamaron.
Jessops have much better service than any of these and know what the're talking about, they also don't lock their cameras away permanently and expect you to not want to play with what you're about to spend a lot of money on. Secondary to this if you do buy from them, get the insurance...