In his stark warning, William Hague claimed that if the independent Scotland wanted to be part of the European Union it would not be able to negotiate the same lucrative terms as Britain rather it should reapply to join the EU.
Scotland is due to hold a referendum for full independence from the UK on September 18 this year.
The allegation made by Hague, meanwhile, comes as Scotland already enjoys a certain level of legal and financial autonomy from London with some powers devolved to the Scottish parliament.
Alex Salmond, First Minister of the ruling Scottish National Party (SNP) has also made it clear that the independent Scotland will retain its EU membership and it will only have to renegotiate the terms.
However, the UK Foreign Secretary says an independent Scotland would be forced to accept the euro as its future currency.
Hague also dismissed Salmond’s confidence about Scotland’s potential place in the EU as unrealistic.
"Alex Salmond can say what he wants, but it would be a very difficult negotiation,” Hague said. “Scots would be paying more to get less from the European Union. There is no doubt about that.”
Hague added that Scotland would effectively have two referendums on whether to leave the EU – “and one of them is in September.”
In response to Hague’s claims, Scotland’s deputy first minister, Nicola Sturgeon, noted that the UK’s planned referendum in 2017 was the only threat to Scotland’s status as an EU member.
Britain’s Conservative-led government has vowed to hold a referendum in 2017 on whether to stay in the EU if it wins the next general election in 2015.