Thanks for all the replies and sorry for the delay in replying. The alarm was professionally installed in the UK and is presumably a UK spec device; it consists of the HKC Quantum 70 and about 8 sensors which are a mix of magnetic, PIR and smoke, it was fitted about 6 months ago and the distance to the furthest remote is probably about 25 ft.
The installer was consulted but advised us that this is an industry wide problem with no solution, other than disabling RF detection - he did change a battery in a central heating thermostat but further advised us that any one of dozens of RF devices (in my daughter's house or one of the neighbours) could be the cause - having Googled the problem it seems that everything from wireless door bells, baby alarms and even car remotes can cause this, which seems ridiculous. Having had a number of full alarms during the night, which scared the living daylights out of the baby, she is now reluctant to set the alarm, and even if she makes sure all her RF device batteries are in good condition she certainly can't police all the neighbours. I will ask her to post the relevant log which she sent to the installer.
Thanks again for all the input.