Image copyright PA Image caption With a week to go before the vote, the rival campaigns were hard at work on Thursday

"It's uncharted territory. That means uncertainty. Years of it. And that's if negotiations go well."

With polls in the UK indicating growing support for Brexit, the mood in Brussels is darkening.

Attitudes are hardening among officials I speak to here.

I'm often asked if the EU is preparing some "gift", a last-minute sweetener to beat the creeping sense of inevitability that Britain could be about to vote Leave in its referendum on the EU.

Until recently, leaders of the other 27 EU members were aching for the UK to stay.

Media playback is unsupported on your device Media caption Katya Adler reports on whether the UK would be safer in or out of the EU

But while Central and Eastern European nations are still keen to be accommodating, France has turned hardline.

"Let them go if they insist and punish them if they do," sums up the sentiment du jour.

This has less to do with Britain, and far more to do with French domestic politics.

France and Germany, the EU's biggest powers, go to the polls next year with resurgent Eurosceptic parties breathing down the necks of the political establishment.

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The penny has dropped among EU leaders that voters want less Brussels in their lives.

Just today, European Council President Donald Tusk said many of the British ideas about the EU were gaining support all over Europe.

But he didn't mean the Leaving idea.

Image copyright PA Image caption The Leave campaign is adamant that it will not accept keeping the UK labour market open to EU workers

The Out sentiment is one Europe's leaders do not want to encourage.

So a gesture pre-referendum or a quick 'n generous new deal for a post-Brexit UK seem unlikely. But would the EU really cut off its nose to spite its face?

Surely outside the EU, the UK would be an attractive trading partner?

"Absolutely," admitted a high level Brussels source grudgingly.

"And Britain probably would get a good deal in the end but no-one here wants to hand it over easily.

"Negotiations will likely take years. And the chances of it getting messy? I'd say they were extremely high."

Image copyright Reuters Image caption European Council President Donald Tusk said on Thursday that a Leave vote would weaken the UK and the EU

The Leave campaign insists it will not sign up to a trade deal that would include having to keep the British labour market open to EU workers - the kind of arrangement Switzerland, Norway and Iceland accepted because they wanted to take part in or be close to the European single market.

But, despite the fighting talk, I have also heard back-room whisperings of possibly, maybe, eventually finding some kind of accommodation for the UK, whereby it could pay a financial "penalty" to be part of the single market without being open to EU migration.

But such scenarios are light years away from where we are now.

If the British public votes Leave next Thursday, all current EU agreements would stay in place for at least two years while the UK disentangled itself from the bloc and embarked on a negotiated settlement with the EU.

But this is uncharted territory and presupposes no unilateral moves from either side.

"If a post-Brexit UK government suddenly of its own accord stopped access for European workers to the British labour market for example," my source told me, "EU countries would likely retaliate. A date could be chosen to simply cut Britain loose.

"If that happened, good luck."

Rambunctious pronouncements aside, the hope in the rest of the EU remains that British voters hold their nose, accept the EU is imperfect, and decide to stay.

As dark as the mood is in Brussels and beyond, it's also fervently felt in many circles that the UK referendum is a clear message that the EU must reform.

Thing is, do you believe it will?