Certainly do. It was an average dry September day (for England) and I was in Coventry at a residential training course for work. The government agency I worked for had just merged with several others and the new bigger audit team was getting to know each other as well as being there for training on our new wider responsibilities.
Now bear in mind the time difference of 5 hours. The morning went just as expected. We found out about it from the buzz around the campus during the afternoon coffee break - that would have been just after the time it happened. I don't remember the rest of the afternoon but I DO remember the evening - there was nothing else to do at the training centre but go to the bar, so we did and there was nothing else on the TV but endless repeats of the footage, American reaction to it, British government expressions of support, I seem to remember the military band at Buckingham Palace playing The Star-Spangled Banner (though that may have been a later day), just anything to say "hands across the ocean, we're with you".
We have a somewhat more relaxed attitude to terrorism having experienced so much of it - I grew up in London in the 1970s when "look out for suspicious abandoned bags or packages, it might be an Irish terrorist bomb" was just a way of life. I nearly got blown up by one in 1983. The Metropolitan Police (think of them as the London Police Department if that helps) are possibly the most experienced in the world over terrorism because of the Provisional IRA (who were partly funded by Irish Americans).
Just out of interest, they are responsible for the rule about liquids in hand luggage on flights, having foiled a plot to blow up planes in mid-flight with liquid explosive in soft drink bottles. I remember that day too - I was flying to Germany that morning and there was this sudden new rule, and when the perpetrators got to court, that's when I found out why. The "Met" had been doing surveillance on the gang for months, but not moved in so as to gather more evidence, and pounced on the day to arrest the lot. I trust those who were convicted are enjoying their very long enforced time off "at Her Majesty's Pleasure".
But by 2001, peace had been achieved and the IRA terrorists had given up. So this came as just as much of a shock to us especially as flying planes into buildings is in a totally different league from just planting bombs under cars or on the public transport. Whatever else we might think of the USA and the daffy Presidents you elect sometimes, we have to unite over that.