UK & Ireland flights

Dave, As the others have mentioned, it is NOT a good idea to purchase budget air tickets "a few days before departure". Budget airlines typically use a "sliding scale", with prices increasing as the flight fills up. Therefore, tickets sold a few days before departure will be in the highest tier. Also, every budget flight I've been on lately has been packed FULL, so if you wait until the last minute, there may not even be seats available. As Nigel mentioned, BE SURE to read their Terms & Conditions carefully. Tickets are often non-refundable and non-changeable once booked (unless you pay for the higher priced "flex fares"). Again as mentioned, EasyJet also has some extra fees but they're much simpler and easier to deal with (IMHO). I routinely travel with EasyJet and will be again in a few months. Be especially careful with luggage weights, as RyanAir especially will nickel & dime you for extra charges and they won't be cheap! If you'll be checking luggage and you think it might be over their allowable weight, it's cheaper to pay for the extra weight at the time of booking rather than at the gate. Also note that many budget airlines only allow ONE carry-on item of the approved size (and they WILL check). It would help to know which routes you'll be travelling? If you decide to book with RyanAir, my condolences. Happy travels!

As you haven't given the routes you are considering it is hard to make detailed suggestions. Don't forget though that Aer Lingus is in effect a LCC over UK-Ireland routes and considering the final cost BA can be competitive especially ex-Dublin.

You'd want to book those flights ahead of time. Their prices often are based on supply and demand, and the longer time out the cheaper the fares.
You also need to anticipate your luggage needs, as paying for a bag when the reservation is made will save you money.

The later you book the higher the price. They go only one way - up. Ryan Air will nickel and dime you to death. Other airlines like Easyjet also have extra charges but they are very easy to work with and less onerous. They also take less glee out of getting every last penny out of you. RyanAir revel in it. In a minute Harold will likely roll up with a song "praising" Ryan Air. It may be a touch over the top, but not far. Easyjet have a pretty decent iOS app. Do read every word of their terms and conditions.

Thanks for the advice. We're flying fm Edinburgh to Dublin.

By request of Nigel, here it is - Fascinating Aida's warning about the perils of Cheap Flights (not safe for work-contains profanity): http://tinyurl.com/2vxmaod "there must be extra charges when the flights are 50p" BTW, I first saw Fascinating Aida perform at the Hammersmith Odeon in December 1985 (my first trip to Europe), so I've been a fan long before this song made them YouTube stars.

Choice between Aer Lingus Regional or Ryanair on that route. Prefer the former myself, if time and price are OK.