Transfer of unused RNRB: The brought-forward allowance: Making a claim.
A claim for brought-forward allowance (IHTM46040) may be made by the deceased’s personal representatives within 2 years ending from the end of the month in which death occurs, or if at a later time, within 3 months beginning with the date on which they first started to act.
If no claim is made by the personal representatives in the time allowed, any other person liable for the tax can make a claim within such later period as an officer of Revenue and Customs may allow in a particular case.
A claim made in either of the periods mentioned above may be withdrawn no later than one month after the end of the period concerned.
Although there is no prescribed form, a claim for brought-forward allowance can be made using IHT436.