BBC reports that the UK's Advertising Standards Authority accepts that Ryanair's advert featuring Winston Churchill did not cause widespread offence.  Apparently, the ad managed to cause 319 complaints,
The Ryanair advert
"We shall fly them to the beaches, we shall fly them to the hills, we shall fly them to London!"

From the ASA's adjudication:
"The Authority acknowledged that the complainants had found the approach extremely tasteless, but noted many media commentators had, in the days that immediately followed the terrorist attacks, commented on the positive and determined response of Londoners to continue with life as normal. Because it noted that response was a source of strength and pride to many, and the advertisers had restricted the theme of the advertisement to the stoical response that followed the attacks, the Authority concluded that the advertisement stopped short of causing serious or widespread offence or promoting further distress.

...The advertisers believed the use of Winston Churchill's image and the parody of his speech were neither offensive nor disrespectful; they pointed out that his response to the bombings during World War 2 was one of defiance and "business as usual". The advertisers believed they had captured the spirit of Churchill and the Blitz mentality of Londoners in the days that followed the terrorist attacks."

Quite right, in my humble opinion.