How do I get the nil-rate band transferred?

In order to be given the transfer, the personal representatives (the person nominated to handle the affairs of the deceased person) of the second spouse to die must make a claim for the transfer within 2 years of the second death.  There is an application form which must be submitted with the other tax papers and this is reviewed by HM Revenue & Customs.  Assuming the claim is accepted, the extra nil-rate band will then be applied to the inheritance tax calculation.