There are only 11 registered on IB's website in UK for the Middle Years (ie GCSE equivalent) programme :
ACS Egham International School
ACS Hillingdon International School
108 Vine Lane, Hillingdon, Uxbridge, Middlesex
Dartford Grammar School
West Hill, Dartford, Kent
Havelock Academy
Holyoake Road, North East Lincolnshire, Grimsby
Hockerill Anglo-European College
Dunmow Road, Bishop's Stortford, Hertfordshire
International Community School
21 Star Street, London
International School of London
139 Gunnersbury Avenue, London
Marymount International School
George Road, Kingston-upon-Thames, Surrey
Southbank International School - Westminster campus
63-65 Portland Place, London
The North London International School
Friern Barnet Road, Friern Barnet, London
United Kingdom Wellington College
Wellington College, Crowthorne, Berkshire
here but doesn't include Sevenoaks
Others offer the Diploma after GCSE/IGCSE instead of A levels.