Royal Mail’s redirection service favours the nuclear family with a pricing structure that is outdated and costly, a consumer group has said.

Citizens Advice said the service is “designed for households of the past” by charging for each surname rather than by household.

Royal Mail said it agreed that a different pricing structure was needed and is currently “working on the details”.

Currently, consumers pay an upfront fee based on the length of time they want to use the service, with three packages ranging from £33.99 per surname for three months to £66.99 for 12 months.

A couple with different surnames would therefore be charged double for the service, “penalising” unmarried couples and spouses who keep their own names, and children and elderly relatives with different surnames, the charity said.

Adding the cost of just one additional surname makes the service more expensive than any other country, its research found.

Citizens Advice, the statutory consumer advocate for postal services, found that more than half of people (55%) who have moved house within the last two years live with at least one person who has a different surname from them.

It found that, since 2012, the price of a three-month redirection has increased by 74%, while second-class stamps have only gone up 12%.

A quarter of those surveyed (26%) said the price was one of the reasons they did not use the service last time they moved.

Citizens Advice is also calling for Royal Mail to make the service more affordable by offering an option to pay in monthly instalments for those who cannot afford a one-off payment, and concessionary rates for consumers on the lowest incomes.

Some 84% of consumers think Royal Mail should ensure its redirection service is affordable for people who need to use it.

The same survey found those who did pay for mail redirection were highly satisfied with the service they received.

According to the Office for National Statistics, 32% of families have “non-traditional” structures outside the married heterosexual couple, such as cohabiting opposite-sex couples, same-sex couples and lone-parent families.

Citizens Advice chief executive Gillian Guy said: “Many people rely on Royal Mail’s redirection service, yet it’s designed for households of the past.

“Consumers are facing a double whammy. Royal Mail has drastically increased the price of redirection over the years but hasn’t changed its outdated price structure that assumes families always share the same surname.

“We’re calling on Royal Mail to change its mail redirection service to no longer charge per surname within the same household. As the dedicated universal service provider, it has a duty to make sure this service is fair and affordable.”

A Royal Mail spokesman said: “We agree with Citizens Advice that there is a need for a different pricing structure.

“We wrote to Citizens Advice last week, before the report was issued, to confirm that we will change the pricing structure of our popular redirections service away from a per surname basis or anything similar.

“We are currently working on the details of this new pricing structure and will share once finalised.”

YouGov surveyed 4,107 British adults online between December 18 and January 17.