@midsomerdave Unfortunately no-one from Vodafone UK is going to be able to help you. Although part of the same group, the two companies have entirely separate administrations, and their systems are also separate.
I've found a Contact Us page from Vodafone PT. Unfortunately Vodafone UK won't let me post the link because it contains a series of numbers which are "forbidden" on this forum, and into the bargain Google Translator doesn't seem to be working on that page, but it says: "Ligar em Roaming – +351 911 691 200 (ou a partir de equipamentos que não suportem numeração curta)" which roughly translates as the number for calling from abroad or from devices which don't support short codes. There's a fair sized expat community of Brits in Portugal, many of whom seem to speak remarkably little Portuguese, so they'll probably be able to put you through to an English-speaking agent.
Do you have a PAYG phone with Vodafone UK? If so, and you opt in for free to Vodafone International, it brings the cost of calls down from £1 per minute to 5p for landlines, or 25p for mobiles - see http://www.vodafone.co.uk/explore/costs/calling-abroad-from-the-uk/
Good luck!
