Staying in the customs union, or any version of it, will leave the UK unable to form new partnerships across the globe, Boris Johnson warns.

Speaking after his visit to Peru, Chile and Argentina the Foreign Secretary says there are "realms of gold" to be won with new trade deals but these can only be negotiated if the UK is able to offer "unhindered and complicated" opportunities.

And he warns the prospect of complex arrangements, tied to existing agreements with the EU, would make it more difficult.

His latest remarks come just days after Mr Johnson warned the Prime Minister she must not betray the country by keeping the UK in the customs union.

It came amid claims that a so-called backstop option to avoid a hard border in Northern Ireland could be used to keep the EU and UK linked by the backdoor.