Hmm, what defines important? I'm going to shoot for aeroplanes which had the greatest impact on the country and community.
Camel, Hurricane, Harrier - the three Sopwith products that massively contributed to winning (or at-least not losing) three wars. The last also bought us a seat on the team producing F-35, and went a very long way to defining the modern jet combat aircraft.
Concorde: trained one generation of aeronautical engineers, and inspired the next generation of engineers and pilots. Also established the paradigm of multinational aeroplane projects, and was the first true FBW aircraft.
Supermarine S6b. Reminded the country what it could do, trained a certain designer in how to build high performance aeroplanes.
Pegasus XL-R: The aeroplane that really brought British microlight production into mass production, and private aviation to thousands of people who otherwise could never have afforded it.
Tiger Moth: How many generations of pilots did this inspire and/or train?, and to some extent, it still is.
de Havilland Comet: Massively significant both for what it achieved, and it didn't. Also pretty much put Britain into the world lead in air accident investigation.
Lynx: Established Britain as a country who could on its own build world class helicopters; we may not have actually done so first, but we've been equal or lead on multiple projects since.
Hawk: Pretty much defined both the modern jet trainer, and post 1970s British defence export practices.
Canberra: Defined the first generation of jet strike aircraft. Also flew the research projects that demonstrated the behaviour of stratospheric circulation and what that meant about nuclear fallout. Pretty good post war exports as well - even the Americans bought it.
R101: Inspired a nation, then in failing ended all large airship development in the Empire and diverted Britain's design efforts towards large aeroplanes. Trained a big chunk of the generation of engineers we'd need in Ww2.
I reserve the right to edit this later and add a few more as they occur to me
Non-inclusions for me. VC10: a superb aeroplane, but one which had minimal national or international impact, essentially because it was designed to meet the requirements of BOAC and nobody else, compared to parallel Boeing aircraft that were genuinely designed to a world market. Mosquito: a fantastic aeroplane, but an evolutionary dead-end, unless you count the plywood fuselage of the Vampire.
G