This is Home Secretary John Reid's message to the nation following yesterday's terror alert.

The events over the last 24 hours have shown that we continue to face an unprecedented threat. What could have happened had the police and security services not disrupted the alleged plot to bring down aircraft through mid-air explosions is almost unimaginable.

As I said just three days ago, we are probably in the most sustained period of severe threat since the end of the war. We cannot be complacent when faced with the kind of people who would target planes full of holidaymakers, including children.

We should be under no illusion that the police believe this alleged plot was a very significant one indeed. So I would like to pay tribute to the skills and professionalism of the police and security services, who are working day and night to prevent terrorist attacks on our soil.

I very much regret the level of disruption being faced by those who are trying to get away for a well-earned holiday or travel to an important meeting and I want to thank the British public as well as visitors from overseas for their fortitude and patience.

We are doing everything we can to minimise the effect on travellers but clearly we cannot compromise people's safety because protecting the public is my paramount concern. That is why the decision has been taken, as a precaution, to raise the UK threat level to the highest level of 'critical'.

But while we must all remain alert, I believe it is vital that we try to carry on our daily business as normal otherwise those who seek to destroy our country, our values and our spirit will win.

We are involved in a long and deep struggle against evil people who don't distinguish between those of different religions, men and women or adults and children.

As a nation of many different communities and religions we stand together in the face of this threat.

So I ask you to remain vigilant and together we will overcome those who wish to harm us.