In this current climate security is a very major factor, however, no matter how good your security systems are the percentages for someone being able to conduct an attack will always be greater than the security forces being able to deter.
With radicalisation being a major factor this means the likelihood of someone who is born in a particular country to succumb to radical propaganda is far greater than it was years ago. As previously it was believed that probable terrorists would infiltrate from other countries.
The UK decided not to have open borders, unlike many of the other countries within the EU, so the likelihood of persons coming in is reduced slightly, but not fully.
So it could be assumed to say the the security threats within the UK are slight less than in the rest of Europe. However, this also needs to reflect the capabilities of the persons on the borders checking who is coming in to the UK and who is going out, for it is not possible to fully check everyone.
If we believe the reports about GCHQ then they could be more robust that some of their European counterparts, but again this does depend on the extent of sharing intelligence, as good, if not excellent intelligence sharing is essential.
The public is reliant on what we are being told.
The best way to reduce terrorism is to be open about the causes and then mitigate the reasons why people are being radicalised, to just assume it is not the fault of the respective countries to some degree is not is a wrong path to take.
To look at the UK, many of the current Tory policies in force and also probably still to come are causing considerable resentment to large section of the UK population. But that is not to say everyone who feels resentment will turn to terrorism, but it should create an atmosphere for the Governments of today and those to come to question their policies and assess the resentments they are creating.
Much of this is down to trust and many within the UK do not trust any politicians of any party. For when it suits your MP will say they are following the will of the majority of their constituents, but then at the bequest of their party leaders they could then discount their constituents and follow their party line. So just whose MP are they their constituents or the party for in many respects they can not be both.
So all countries need to seriously look inward and be objective whether the paths they are choosing to go down have some serious bearing on persons being open to be radicalised for borders whether they are open or closed or the effectiveness of the security operations are but only two of the many reasons for radicalisation to occur.
More can always be done, do not rest on your laurels.