Guideplus stopped transmitting on ITV1 analogue 1st Jan 2011.
You can try and change the setup of GuidePlus (the tab option far right when EPG is displayed next to Schedule) and change to use a digital receiver and channel Bid TV.
Have also seen this suggested:
The trick to getting the Philips to start looking for the bid-tv data is to go to the well hidden 'SetUp' tab at the far right of the EPG. Go to 'Start Installation'. This may lose any future recordings you had set, but won't factory reset or wipe progs you've recorded.
Philips say to set a false postcode (a different region to the one you're in) for today. Then tomorrow, come back and reinstall again, this time saying your true postcode.
Mark, January 2011