Carnivor is right.
Go to System Preferences, Date & Time and check that your Time Zone is set to London. Then Google Search in iPhoto will start off in London.
Not only am i right (gloat) ive sorted it out
Use Google Earth to get the coords you want to use.
Show Package Contents of DateAndTime.prefPane
Show Package Contents of TimeZone.prefPane
open all_cities_adj.plist
I edited the London setting to reflect Bristol, I only changed the Bold settings,
<array>
<string>
51.500000</string>
<string>
-0.166656</string>
<string>11</string>
<string>Europe/London</string>
<string>GB</string>
<string>
London</string>
<string>England</string>
</array>
Save All and goto date/time timezone, Now you can pick Bristol - England
Im everso slightly out on the coords but iphoto now shows Bristol as its default location instead of London or Cardiff,
ohh btw, London is the only city in England so you can search for England to find that array.
edit: forgot to mention, I editied London on this occasion but it would be easy enough to add places instead of renaming them