As said, with windscreen cover, ie, glass cover on fully comp policies, you can claim as much as you like - it's like a seperate policy comparred to the car one, as in it won't affect your NCB or boost your premium....
A 1997 Escort will be whats known as a 3545 screen - so depending on if you have a top tint (only available IIRC is a blue top tint on a green screen) you would have a 3545AGNBLHV (or 3545AGNHV for non top tint)
Fitting is usually piece of piss on these - takes about half hour to 45mins, but you won't be able to do it yourself unless you have access to the proper bonding stuff - an no, silicone will not work
Depending on your insurance company, your two firms for insurace work are RAC Autowindscreens or Autoglass, and the your local branch in Dagenham would be our Romford branch....
You can get second hand screens for these, but I am always very weary of them as you have to be a) good, and b) super carefull to get them out without a) breaking the screen, and b) damaging the heater element and connections.
You're always far better off with a brand new one fitted by a company as at least then you have comeback if anything don't work, or you have any probs. IE, with us (autoglass) you are covered if the heater element is at fault (we replace screen for free) is it leaks (we remove and refit it for free) or if you get windnoise etc (again we remove and refit for free)