Suffix Letters (1963 - 1983)
| Reg | Start of Reg. | End of Reg. |
| A | 1st Feb. 1963 | 31st Dec. 1963 |
| B | 1st January 1964 | 31st Dec. 1964 |
| C | 1st January 1965 | 31st Dec. 1965 |
| D | 1st January 1966 | 31st Dec. 1966 |
| E | 1st January 1967 | 31st July 1967 |
| F | 1st August 1967 | 31st July 1968 |
| G | 1st August 1968 | 31st July 1969 |
| H | 1st August 1969 | 31st July 1970 |
| J | 1st August 1970 | 31st July 1971 |
| K | 1st August 1971 | 31st July 1972 |
| L | 1st August 1972 | 31st July 1973 |
| M | 1st August 1973 | 31st July 1974 |
| N | 1st August 1974 | 31st July 1975 |
| P | 1st August 1975 | 31st July 1976 |
| R | 1st August 1976 | 31st July 1977 |
| S | 1st August 1977 | 31st July 1978 |
| T | 1st August 1978 | 31st July 1979 |
| V | 1st August 1979 | 31st July 1980 |
| W | 1st August 1980 | 31st July 1981 |
| X | 1st August 1981 | 31st July 1982 |
| Y | 1st August 1982 | 31st July 1983 |
Prefix Letters (1983 - 2001)
| Reg | Start of Reg. | End of Reg. |
| A | 1st August 1983 | 31st July 1984 |
| B | 1st August 1984 | 31st July 1985 |
| C | 1st August 1985 | 31st July 1986 |
| D | 1st August 1986 | 31st July 1987 |
| E | 1st August 1987 | 31st July 1988 |
| F | 1st August 1988 | 31st July 1989 |
| G | 1st August 1989 | 31st July 1990 |
| H | 1st August 1990 | 31st July 1991 |
| J | 1st August 1991 | 31st July 1992 |
| K | 1st August 1992 | 31st July 1993 |
| L | 1st August 1993 | 31st July 1994 |
| M | 1st August 1994 | 31st July 1995 |
| N | 1st August 1995 | 31st July 1996 |
| P | 1st August 1996 | 31st July 1997 |
| R | 1st August 1997 | 31st July 1998 |
| S | 1st August 1998 | 28th Feb. 1999 |
| T | 1st March 1999 | 31st July 1999 |
| V | 1st August 1999 | 29th Feb. 2000 |
| W | 1st March 2000 | 31st July 2000 |
| X | 1st August 2000 | 28th Feb. 2001 |
| Y | 1st March 2001 | 31st August 2001 |
New style (2001 onwards)
| Reg | Start of Reg. | End of Reg. |
| 51 | 1st Sept. 2001 | 28th Feb. 2002 |
| 02 | 1st March 2002 | 31st August 2002 |
| 52 | 1st Sept. 2002 | 28th Feb. 2003 |
| 03 | 1st March 2003 | 31st August 2003 |
| 53 | 1st Sept. 2003 | 29th Feb. 2004 |
| 04 | 1st March 2004 | 31st August 2004 |
| 54 | 1st Sept. 2004 | 28th Feb. 2005 |
| 05 | 1st March 2005 | 31st August 2005 |
| 55 | 1st Sept. 2005 | 28th Feb. 2006 |
| 06 | 1st March 2006 | 31st August 2006 |
| 56 | 1st Sept. 2006 | 28th Feb. 2007 |
| 07 | 1st March 2007 | 31st August 2007 |
| 57 | 1st Sept. 2007 | 29th Feb. 2008 |
| 08 | 1st March 2008 | 31st August 2008 |
| 58 | 1st Sept. 2008 | 28th Feb. 2009 |
| 09 | 1st March 2009 | 31st August 2009 |
| 59 | 1st Sept. 2009 | 28th Feb. 2010 |
| 10 | 1st March 2010 | 31st August 2010 |
| 60 | 1st Sept. 2010 | 28th Feb. 2011 |
| 11 | 1st March 2011 | 31st August 2011 |
| 61 | 1st Sept. 2011 | 28th Feb. 2012 |
| 12 | 1st March 2012 | 31st August 2012 |
| 62 | 1st Sept. 2012 | 28th Feb. 2013 |