Im in the Midlands (Burton) and rang around dealerships at the start of the year to get an idea of prices for the upcoming 24k service:
Burton - 24k £220, 36k £350
Wolves - 24k £174, 36k £264, 72k £839!! (also told they needed 10 days notice if you want a courtesy car!)
Leicester - 24k £200, 36k £300
Solihull - 24k £170, 36k £310, 48k £170
Prices probably gone up now but gives an idea of who is cheaper. Best to ring around yourself. Get the phone numbers from Google.