How can I get to Luton Airport from Watford via public transport?

As I have done the trip a couple of times now, here's how it goes:

I took the 321 from Watford Town Centre (do check the exact bus stop and times on Arriva's website) and asked the driver to give me a ticket to Luton Airport. It will be a special ticket (as of January, 2016 it costs 5.10 pounds one way) that will allow you to get to Luton (specifically Luton Rail Station Interchange) and then get another bus - service 'A' - that can take you to Luton Airport.

The ride from Watford to Luton is quite long as the 321 passes through loads of villages and St Albans on the way. I'd reserve 2 hours and a half just for the journey to the airport.

This can be done when returning as well, just ask the 'A' bus driver for a ticket to Watford.

01/2016 - EDIT: Luton Airport is currently undergoing renovations. The new bay for catching the A bus is sorta towards the car park (I believe it's bay D now, it was one of the last ones, just past the Greenline bay).

Somewhat counterintuitive (ie heading off in almost the opposite direction) but Watford to Baker Street by Metropolitan Line is about £12.60 (standard single, may be less) and about 40 minutes. Baker Street to LTN by easyBus is from £2 and takes about 1 hour - so perhaps about 2 hours and £15 in total.

I've done the walk from Church Street in Luton up to the airport before. It's not going to win any awards for "picturesque walk of the year", but as long as you're fit it's fine. There's a massive hill to walk up, but there's footpaths and lights along the whole way. 25 mins seems a little short to me though, I'd allow a tiny bit longer

However... Church Street in Luton is where almost all the buses go to. As such, there's lots of buses which'll get you up to the airport you can catch from there. Expect to spend a couple of quid on a single ticket.

One other option - it's a 5 minute walk from Church Street to Luton Station, then a couple of minutes on the train down to Luton Airport Parkway, from which you can get an express bus to the airport. Probably only worth doing if you're trying to travel at a time of day when the local buses from Luton to the Airport aren't frequent enough

Train from watford junction station to St Albans Abbey and walk up the hill to St Albans main line direct to Luton parkway bus included from parkway to Luton Airport about £11

To avoid the hassle of transiting via Church St, you could opt for a bus-train combination via Radlett.

• Uno bus 602 runs hourly from Watford High Street to Radlett. Travel time: ~ 30 mins
• From Radlett take any train to Luton Airport Parkway and continue with the airport shuttle. Travel time: ~ 30 mins