This one is up for debate, as far as I know no consensus has been reached. Extratropical activity in Europe is far from rare; indeed the UK is a dumping ground for the remanants of once tropical storms or hurricanes. What is rare is actual verified tropical activity over Europe. There is only one undisputed example of this ever happening, and that was the 2005 storm Hurricane Vince, which was still a fully tropical depression when it hit portugal. The most northern tropical storm ever was Hurricane faith which was about 61 degrees North when it lost its tropical status, however this one did not make landfall with Europe before it became extratropical.

Debbie formed at 15degrees North west of the African continent on the 6th of September 1961, favourable conditions including low wind sheer in particular allowed the system to very quickly become a hurricane, it maxed out as a catogary threeon september 12th. This was the point it quickly accelerated NE while weakning to a catogary 1, and contrary to forecasts headed for the W coast of Ireland. The storm had hurricane 1 force winds and gusts in excess of 100mph were felt in Ireland and N ireland, aswell as britian. The storm caused flooding, structural damage, and caused massive waves to hit the coastal areas. 

Now the issue is there is some debate about exactly when the storm lost tropical characturistics; either on the 15th or the 16th, if the later is true then it is the first and only hurricane ever to hit the british isles and Europe, and only the 2nd tropical system ever to hit Europe, and if it is the former then Vince still holds the title as the only tropical system ever to Hit Europe. 

Below are some interesting images:

NOAA, wunderground, wikipedia

What do people think?

The thing is though, some sources consider it extratropical just before it hit the british isles; I can't find any agreement about which it was unfortunately. Still if this storm was not extratropical then it beats Vince because this would be a Catogary 1 hurricane or at the very least a Tropical storm. Another possible debate that I haven't brought up involves Faith and the Fareo islands, although it seems to be more generally agreed that Faith was extratropical by then. A further less contentous one is 1967 Hurricane Chloe which arguably hit the N coast of Spain and Western France as a tropical storm/depression. Again this one causes less debates because it seems to be more agreed upon that it was just extratropical by then. Interesting stuff anyway, I think if this says anything, it says that hurricanes are possible in Europe and Britian, just very rare possibly occuring less than 1 every 300 years. 

And in fact on that point, I suspect the closest thing we experience in the UK to a hurricane in terms of structure is the winter polar low, given its non-frontal, closed circulation features!

Hurricanes can have frontal features even in the tropics, a single warm front trailing is not that rare. But granted the picture posted by Kev on the 16th looks like a mid latitude storm. Nevertheless on the 15th it was undisputadely a storm, and that would have been 24 hours before that at the most. The actual storm is just the circular part which only contains the tip of the fronts, so idk. Interesting point about polar lows, although they do tend to contain troughs, if not fronts, which give rise to sharp thin bands of showers rather than spirial. 

Q, developed polar lows are typically characterised by a spiral structure with a clear eye in the middle, not shower banding which is more typical of troughs. More info here:

http://www.weatheronline.co.uk/reports/wxfacts/The-Polar-low---the-arctic-hurricane.htm

Oh wow, they really do look like hurricanes.