How to top up Three PAYG SIM from abroad
 

The UK adopts a very rigid top up scheme for foreigners:
You either have to hold an UK-issued and -registered credit or debit card or buy top up cards in the country.

I want to keep my Three SIM alive from abroad and top up for a Three like home roaming country.

Is there a way besides some dubious online angencies charging about 20%? On Ebay.co.uk I can't find vouchers anymore.

Wondering why the UK adopts such an approach, I was told because of credit card fraud. But they accept and refuse debit cards too. Where is the risk of preloaded debit cards like Neteller or Entropay?

May be anyone knows a way or a credit/debit card generally accessible that would work? What about a UK-issued "gift" prepaid Visa or Master?

With UK SIM cards, you don't need to top up to keep them active. A balance deduction (e.g. a roaming SMS or an incoming roaming call of one second for 1p) every 6 months will suffice.

Nevertheless I sympathise with your frustration at the refusal of non-UK cards. Such policies are not objectively justified and are in keeping with many British companies' insular mentality of surcharging or impeding anything foreign.