Why are the benefits of joining a £12 trillion Pacific trade bloc so tiny?

Reading the small print reveals the downside, Jon Stone explains

Trade secretary Kemi Badenoch (PA)

The government has been keen to trumpet the benefits of Britain joining CPTPP – a major pan-Pacific trading bloc. The bloc's economies are worth £12 trillion, a huge amount. Mayor players in the club include Australia, Canada, Japan, Malaysia, Mexico and Vietnam.

However, read the small print and the benefits to the UK from accession are tiny, just 0.08 per cent GDP growth over 10 years.

How can there be such a disconnect? A new piece of research by the UK Trade Policy Observatory at the University of Sussex helps explain why the benefits are so small.