Nearby is a great UK info-mashup! - Nearby.org.uk is a site with heaps of UK (and Ireland) location based information. They have taken this information and created a customizable mashup application with a huge list of on-demand information layers you can overlay from various UK sites. Example site-feeds include info from wetroads.co.uk, cavedatabase.co.uk and Ports.org.uk to name a few. Also features Google Earth integration. (NOTE: This mashup works best in Internet Explorer)
BlueGhost features Weather, traffic and rail info - BlueGhost UK Info was born out of the BBC Backstage Project and features real-time various information overlays for the UK on Google Maps. Toggle national weather, traffic and rail alerts on the Google Map. Interestingly, this is the first mashup code I've seen making use of the new zooming feature recently added by the Google Maps team. [via]
Google Maps ADSL Availability Checker - Here's a mashup that combines an ADSL availability checker with Google Maps. Type in a UK postcode and a map is displayed showing the distance from that post code to the local telephone exchange. This distance is then used to calculate the maximum speed of an ADSL connection and a list of broadband providers in the area. Start here if you want to reference a postcode. The above link shows an example result.
Other UK Google Maps Mashups:
Green Brighton - vegetarian and vegan restaurants, organic veg boxes, recycling centers, permaculture gardens and meditation classes.
UK Handbag Theft Map - (Only works on Internet Explorer)
UK Speed Cams
Tap Water Quality for fish tanks
UK Knickers Map - More info here
Exeter College Campus
Mapperz - An excellent maps blog that covers many UK-based Google Maps sites as they are launched
Check out Part 2 of the UK Google Maps Mashup Roundup!