Ladies and Gentlemen, will people please learn to use the correct prefix when operating under CEPT rules.
The prefix for CEPT operation in Madeira is CT9 not CT3. Likewise the correct prefix for the UK now starts with M not G.
Now the world will not end because the wrong prefix was used but if you use the wrong callsign you are technically operating without a licence and the SOTA MT could insist the chases and activation are not valid.
And UK stations MUST drop the RSL i.e. you become xx/M0FMF and likewise I am forced to use xx/G4ONL, hence the reason for my other callsigns.
73 Victor G(#)4ONL / EI7KP / OK8VM
Also please check which end you attach the local country’s call letters as defined in the relevant agreement. In CEPT TR61/01 that is prior to your callsign in all signatory countries EXCEPT PERU who want the OA and region number AFTER your home call sign. This latter format is more common in individual bilateral agreements between countries outside of the CEPT agreements.
The moral of the story - as always, read the documentation and rules before your trip so that you know.
73 Ed.
I have enough trouble with remembering to swap between M5 and MW5 and back again, especially when a SOTA day goes across the border. Of course on summits like GW/SW-041 I can stand with one foot each side of the border and be right every time 
I remember having trouble figuring that out last time I visited Australia. At the time, the ACMA site was saying one thing and the WIA site was saying something contradictory. This was a few years back, though, and, as far as I can tell, the rule is now to use VK/.
Hi Rick,
As you were operating under the CEPT agreement in Australia - the details in that agreement TR61/01 say that the extra letters come before your home callsign for temporary operation in Australia. I believe the text on the WIA website was from the days when there were individual reciprocity agreements with countries and for example with the US, I seem to remember when I researched this, that they said home call/suffix.
However … Whatever is stated on the national regulators’ website - in this case, the ACMA - overrides everything else.
73 Ed.
https://www.acma.gov.au/licences/overseas-amateur-visiting-australia-class-licence
Overseas visiting amateurs must use their call sign with a “VK” in front of it to show their location. Section 11 of the class licence has more information using your overseas call sign.
It was a few years back, but the WIA site was the one that seemed to be ahead of the game at the time, while there was a bit of a muddle on the ACMA site. (TBH, having had a quick look at it today, the ACMA site suffers badly from having been written in lawyerese, and does a good job of being as clear as mud to non-lawyers…)
And the ACMA site has that lovely feature of no document ever being retrievable a second time using the original URL.
I didn’t say this, but whatever you do could be right or wrong, but you can be sure nobody will care either way. No money in regulating amateur radio.
73 Andrew VK1DA/VK2UH
And where does that sit on the “how to gain friends and influence people” scale? 
Not as far below the keynote as it would be if “could” was substituted by “will”!
My opinion is that it is not the duty of the MT to enforce the rules of every country that participates in SOTA, but a little reminder now and again does not go amiss. After all we don’t want to be accused of encouraging scofflaw behaviour!