The DEFRA website should be your first port of call, this gives you a complete list of all the routes, carriers, and up to date requirements. Whilst it is easier to fly dogs within mainland Europe, dogs flying into the UK, must be brought in as cargo, no option to do it as excess baggage. A way that many people use to get around this, is to fly to either Brussels or Paris with the dog in the hold as excess baggage, much much cheaper. From there, it is a short hop over the Channel, but of course you need someone to collect you, as only pets in vehicles are allowed on these short crossings. The only route I am aware of where you can travel as a foot passenger with your dog, is the longer crossing from Hook of Holland to Harwich, but quite alot more expensive again than the short Channel hop.
Keep checking with the DEFRA website, as things are always changing. Doncaster has been added recently as a recognised route, Bristol, Manchester, Gatwick and Heathrow are recognised too.
Train travel in Europe is also an option, though I wouldn't recommend a long journey by train as it could be difficult for a younger dog, but from Paris (Airport) to Calais is again a way to get closer to British Shores before your friendly car driver collects you for the last leg of your journey.