Regular expression for UK postcode

I’m looking for an answer to my regular expresssion problem in c#. I’m looking for a match on a specific postcode format and have run into problems. Here you can find my solution with the regex pattern.

C#

public bool IsPostCode (string postcode)
{
    return (
        Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") ||
        Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][0-9][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") ||
        Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][A-HK-Ya-hk-y][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") ||
        Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][A-HK-Ya-hk-y][0-9][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") ||
        Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][0-9][A-HJKS-UWa-hjks-uw][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") ||
        Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][A-HK-Ya-hk-y][0-9][A-Za-z][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z{2}$)") ||
        Regex.IsMatch(postcode, "(^[Gg][Ii][Rr][]*0[Aa][Aa]$)")
        );
}

Visual Basic

Public Function IsPostCode(postcode As String) As Boolean
    Return (Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") OrElse
                Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][0-9][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") OrElse
                Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][A-HK-Ya-hk-y][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") OrElse
                Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][A-HK-Ya-hk-y][0-9][0-9][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") OrElse
                Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][0-9][A-HJKS-UWa-hjks-uw][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") OrElse
                Regex.IsMatch(postcode, "(^[A-PR-UWYZa-pr-uwyz][A-HK-Ya-hk-y][0-9][A-Za-z][ ]*[0-9][ABD-HJLNP-UW-Zabd-hjlnp-uw-z]{2}$)") OrElse
                Regex.IsMatch(postcode, "(^[Gg][Ii][Rr][]*0[Aa][Aa]$)"))
End Function

Happy coding!