A decision to prevent entry to the UK may be made at the entry clearance application stage, or when a person arrives at the port of entry. Additionally, prevention of entry on grounds of criminality may include foreign national prisoners who have either been deported from, or removed and subsequently excluded from, the United Kingdom.
There are no centrally held records that encompass the total number of foreign nationals who have been prevented from entering the UK, but I can confirm that since July 2005 the Home Secretary has excluded 163 individuals from the UK on the grounds of national security and 106 individuals on the grounds of unacceptable behaviour.
I can also confirm that 2,852 individuals were refused entry at the UK border on non-conducive grounds between 2005 and 2008. Figures for 2009 will not be published until the end of year.