well I answer this one myself for anybody who might be interested! I got two quotations yesterday-- E100 for both visits from one individual who told me he cant show qualifications/ or insurance, nor is member of body of installers! The second quotation was E90 callout charge for day one, and e90 call out+ one hour's work day two, ( but it will probably be more than one hour day two).
Today a guy called whom I saw recommended here on this site- Soundtech marino--his view is, its too old a system --get a new one!! minimun e900..... BUT for absolutely nothing he disabled whats there so builder can go ahead and build porch.. Its an unfortunate extra cost to porch, but guess who I am going to get to do the job unless I find someone else substantially cheaper than that for a new alarm for whole 3bed semi.... what do you guys think?