The default weather application for the iPhone uses the yahoo weather service rather than the UK’s National Weather Service the Met Office. UK Weather is a tweak to get official Met Office weather information on the iPhone including in the Notification Centre. It requires the iPhone to be jailbroken. It also provides Met Office weather for some other jailbreak applications including Weather Icon and Weather Plugins for LockInfo as well as WinterBoard lock screen themes that use yahoo weather data.
There are no new icons added to the homescreen. Configure options from the Settings app