I don't think there's any prescribed phrases in CAP413 for that situation. However "G-ABCD switching to XXX. Back with you in five minutes" works for me. At the very least I hope the ATCO will not throw away the strip so that I don't have to "pass my message" in whole again.

You can simply ask for a temporary frequency change, instead of asking/telling them you're changing frequency. Usually works for me :)

Of course the LARS provider can then say "Freecall XYZ information, squawk 7000, good day" ;)

I have used the "temporary frequency change" method in the past and it works for me; usually along the lines of BackPacker's radio call.

I was taught it's always a good idea to call up any nearby airfields, controlled or uncontrolled, along your route in order to gain traffic information, weather or any other pertinent details. My call usually is along the lines of a typical TPAIR call, adding at the end "will be passing through your overhead/x miles abeam North/South/East/West in x minutes, will report crossing the overhead/abeam the field". Certainly any units I've used this with seem very appreciative of this. Especially useful if you are going anywhere near parachuting sites or if the airfield in question is busy. Then once you're past the airfield you can change back to the LARS/FIR provider you were originally using.

Smithy.

Thanks for the info.

Probably the worst piece of advice I ever heard given was to a student whose QXC route took her through the Shawbury CMATZ twice. She was told that she need not bother to talk to Shawbury, strictly true but an incredibly stupid piece of advice given the area through which she would be flying. For those who don't know, Shawbury is a very busy CMATZ (busier than a certain apparently anti-GA airport not a million miles away) which handles both a very large amount of Military Air Traffic in their local AIAA and civilian traffic. It is also the Military ATCO School. The ATCOs at EGOS are, in my experience, always unfailingly polite, patient and very helpful and a real pleasure to deal with. I know some people have a bit of a hang-up about talking to Mil ATCOs but it is an unfounded fear. I would always talk to a MIL ATCO, probably in preference to a civilian one as I know I will be treated courteously and not simply have "Remain clear of controlled airspace" barked at me, that is if I manage to get a reply other than "I'll get back to you" (that last was before I had even been asked to "Pass your message").
So, if you are near to a MATZ talk to them, you will probably be very pleasantly surprised by the way you are dealt with.

My instructor once laughed at me, when I told him that I did precisely that - out of improvisation - during a solo XC.
He told me to expect to repeat the whole radio call again, when coming back into the LARS frequency, and receive a new squawk every time.
I'm glad to see that I wasn't completely wrong, after all!

Even better, if you are equipped with 2 COMs, speak to the airfield on your Box 2 ! :)

Deeday: Technically there's nothing wrong with what your instructor's saying but most, if not all radio units aren't bothered with that and will happily keep your details and wait for you calling back in 5 minutes' time. Saves you having to do long-winded calls and saves him/her writing out your details again :\

My view would be to always call up the ATSU if I'm ever going near an airfield, especially a Mil unit where there may be some "interesting" traffic moving at speed in the local area...

Smithy

I would still stay with the LARS controller...I've had an uncontrolled field say "no known traffic" when I checked in with them, just as one appeared head on not very far away.

Don't be lulled into a false sense of security when talking to a non radar equipped unit.