It’s rare indeed for Prime Ministers to spring genuine surprises. So much of politics is governed by leaks and briefings that to keep the news of a snap general election secret has been a major achievement.

But does it make sense for Theresa May go to the country right now?

She says she needs a mandate for Brexit - but she already has that form the June referendum. There is no serious opposition to Brexit in the Commons or even in the Lords. Article 50 went through without a hitch. The Supreme Court said the Scottish Parliament has no right to interrupt the course of Brexit. Labour has only offered token resistance to hard Brexit.

Theresa May has always argued there is no justification - “no ifs no buts” as she said on the BBC’s Andrew Marr show - for a general election and she was right. The government has a comfortable majority in the House of Commons.

She also repeatedly insisted that “now is not the time” for a referendum on Scottish independence because Britain needs a period of stability in order to make a success of coming our of the European Union.

Well, that also applies, surely to an early general election. Nicola Sturgeon will have her own thoughts on that.

The real reason for this election is, one suspects, because the government realises that it is losing the argument, not in the House of Commons, but in Brussels. The course of Brexit is proving much more problematic than the breezily optimistic Brexiteers said it would be last June.

They insisted that the EU would roll over and allow the UK unrestricted “frictionless” access to the European Single Market. This is clearly not going to happen. We are heading for a very hard Brexit indeed - essentially reverting to World Trade Organisation rules which means tariffs being raised on British exports and the restoration of regulations that inhibit British services, like the financial sector, operating freely in the single market.

Scotland clearly was also in the Prime Minister’s mind. Mrs May realises Ms Sturgeon has a very strong mandate in the Scottish parliament and that the Scottish Government is going to do its best to interrupt hard Brexit, even though Holyrood has no legal right to impede Article 50. Number Ten clearly foresees problems ahead on the Great Reform Bill which will repatriate Brussels law to the UK parliament.

There is a legal argument that powers over matters like agriculture and fisheries should go by default to the Scottish parliament. But that would impede the creation of a UK wide single market.

Mrs May is seeking a mandate that will overwhelm the rival authority of the Scottish Parliament. It will allow the UK government to decide on the future of the powers repatriated to Britain.

The Scotland Act is therefore very much in the firing line here.

The First Minister hasn’t spoken yet, but if this snap general election is a new referendum on Brexit, then it also looks like a new referendum on independence.