Passport checks could become mandatory at Scotland's border with England if the country votes to become independent, says Britain's Minister for Europe.
During a visit to the Scottish Parliament in Edinburgh on Monday, David Lidington, said that by becoming independent, Scotland would automatically become part of the Schengen Agreement which bans free European travel between countries which are part of the agreement and those that are not.
As Britain has opted out of this agreement, Scottish independence would necessitate border controls between the two countries.
Mr Lidlington said that Scotland would need to negotiate its own opt-out from the Schengen Agreement, but this would require the unanimous assent of all other member states.
But Alex Salmond, Scottish National Party (SNP) leader, has accused the UK of "scaremongering". He has previously claimed that Scotland would automatically inherit the UK's opt-outs, removing the necessity for border posts - but this has yet to be verified.
Willie Rennie, Scottish Liberal Democrat leader, urged for clarity at the meeting, saying: 'Passport controls between England and Scotland would have a significant impact on the ease of travel between our two nations."