So after monitoring the wifi over the last 2 week there was a big improvement.
The router rebooted every couple of days at 8am and 2am.
Last night i got round adding my ipod and work tablet to the replacement router and that night it started doing what I was complaining about otiginally. rebooting over and over 7 times in total in the the space of of a couple of hours.
Everything seems sorted till i put the tablet on the my wifi network last night. Not sure if it coincidence
Remove all devices from the system (switch off) then connect the tablet, do a bit of surfing for half an hour and if there are any problems report them back with time of day, and we can see if they match any spikes on the BQM.