Hubby and I plan to spend 5 weeks mid Sept-mid Oct. Is it best to fly from San Francisco to London and then to Scotland where we will rent a car. Can we take car to Ireland?. Is it best to back track and return car to same area we pick up and then back to London to fly non stop to San Francisco? Is 5 weeks enough time to leisurely travel to areas of interest, countryside and let hubby play a few rounds of golf? Our first trip outside of the US. We are both in our early 60's.
I'd suggest first narrowing down what you want to see/do in both Ireland and Scotland and then plan your travel accordingly. On a trip like this I would recommend flying open jaw - into one city and out of another. One suggested route would be - fly to Shannon Airport in Ireland. Pick up a car there and then drop off before taking the ferry to Scotland. Car rental fees to take car from Ireland to Scotland (if still allowed) are very expensive so you're better off dropping of the car and then renting another when you get to Scotland. From Scotland, you could then take the train to London and then fly home from London. Another option is to fly from Ireland to Scotland - those decisions however should be driven by what you want to see/do on your trip! As far as "leisurely" it really depends upon what you want to see - although the British Isles are smaller than the U.S. - it's still a fair bit of country. Also, once you get out of the major cities in both Scotland and Ireland, bear in mind that it does take a bit longer to get from "point A" to "point B" than the mileage would indicate. To give you an idea of time involved, my husband and I did a two week trip to the highlands of Scotland - took almost two weeks to go along the coast from Glasgow to Edinburgh with a 3 day trip out to Orkney.
Most car hire companies will not permit you to take a car from Ireland to Scotland/ Wales, so go for two separate hires. The one way drop fees would also be high.
Work out for your dates, budget and itinerary whether taking the ferry or flying would be your best option. Take the train between London and Scotland. Hiring a car will be slightly cheaper if you return it to the same place in Ireland and Scotland.
I spent 4 weeks last year just touring part of Scotland, so a 5 week trip is ok, but if you want, say, a week in London, that only gives you 2 weeks each for Ireland and Scotland, which isn't a long time to cover quite a lot of ground. For a trip of this length, try to stay at least 4 nights in each location to avoid the feeling that you are in transit the whole time.
Flights between Scotland and Ireland are frequent and convenient. Unless you really love ferry boats and want to spend the extra time going by ferry, I'd say fly.
5 weeks is lovely...just not for 3 destinations. I suspect you will feel a little rushed trying to fit all 3 in. We're taking 14 days to do Edinburgh(4 nights) and the Highlands(Inverness, Skye, Mull, Stirling) and with the exception of 3 nights in Skye, that only gives us one complete day in each of the others. I suspect you would have the same issue with either two weeks in Scotland or Ireland. My ideal would be at least 3 nights in each location. But, it can be done, though you will have to be quite regimented in your timing and not dawdle along the photogenic routes! I have been told over and over that Google times between destinations in the Highlands are very optimistic. Your trade-off might be fewer locations along the way and more time in each.
We are going back to Edinburgh several months later for the Royal Edinburgh Military Tattoo and then training down to London for a week there(minus two nights in Oxford and one night in Salisbury(Stonehenge) and even that is going to be hectic. From Canada, I know most of our flights stop at Heathrow anyway and switch planes for the onward trip to Edinburgh(not sure about Glascow or Ireland though if that's where you're flying into). For example, the second trip we are flying into Edinburgh(via London) and out of London.
I do agree with the "fly into one-out of another" in this case; you might want to look at Celtic Legend Car Rentals(they use Arnold Clark Car Rentals); and serve both Scotland and Ireland. Willie Wallace gives you very personalized service and good rates(even for automatics) and a no bs website. That's who we have booked with.
You will have to shorten your list of things to see as you have a lot of ground to cover. I did separate trips of Scotland and Ireland each for three weeks and still wished I had a lot more time in both. You don't have to fly in and out of London, I would actually try to avoid it if possible. Try finding a direct flight into Dublin, or fly into Edinburgh via Amsterdam, both airports are smaller and much easier to deal with than Heathrow. Flying in to Shannon may also be a better choice for you, but you may not find a direct flight. A good option might be to fly into Dublin, do that tour, then either take a short flight or ferry ride to Scotland, finish in Edinburgh or Glasgow then either take a train or short flight to London and finish your trip there. If you aren't pressed for time the train ride from Scotland to London might be a good way to see some of the countryside and relax a bit.
If staying in London as tourist, I would recommend taking the train, versus flying, to Scotland. Rail service is frequent and considering the time it takes fly (counting getting to the airport 2 hours ahead of time, etc.) you ride the train faster and more comfortably. If you purchase tickets in advance (90-120 days), it's also pretty affordable. The trip from London Kings Cross to Edinburgh is about 4.5 hours and WIFI is available. I found the trip rather pleasant...
I would also look into flying "Open Jaw" instead of back-tracking to London to return home. You should be able to find just as good of deals flying into London and out of an airport in Ireland.
I would only rent a car on an as-needed basis during your travels. You'll be surprised at just how accessible, via public transport, the UK and Ireland are. Exceptions are the Cotswolds & Hill District of England, 'Interior' of Wales, Highlands in Scotland, and 'Interior' of Ireland (among others).