TSEM9852 | Form 17 rule - how couple make declaration
From HM Revenue & Customs · Trusts, Settlements and Estates Manual
A declaration can be accepted only if made on form 17.
The form must be signed and dated by both spouses or both civil partners, but can be sent to the tax office of either spouse or civil partner.
The declaration sets out the property and income they want the declaration to cover and states the interest each spouse or civil partner holds in
each item of property
the income produced by each item.
Once a declaration is made it remains in force until the couple’s interests in the property or income change, or they stop living together as a married couple or as civil partners of each other.
No split other than 50/50 can be accepted until a satisfactory declaration is received.