Second method avoiding the credit/administration fee.

Hi flyers, or as one word if you wish.

I usually pay for my flights using my pre-paid mastercard, as any intelligent person who knows ryanair would. But on this occasion I had the flights but not my mastercard.
And I'm also having problems getting a new pre-paid mastercard, since the company I am using won't issue me another card using the same name (photo proof of identity required). This will no doubt take time, time I don't have when I see the 1 day madness on ryanair's website.

So I had the flights but not the card, £20 return from Manchester - Faro, but this had initially jumped to £24 return. (after purchase this had jumped to around £60, he).
I didn't want to pay £36 for flights, I would rather pay the base fare of £24 and let that be that. So I originally thought about this idea I had thought about a few months ago, 'voucher'.

I immediately went onto ryanair.com to purchase a £25 voucher, filled out my name, debit card details and the total amount including the unavoidable charge of £5. So £30 for a £25 voucher

The voucher can only be redeemed once, so if you've got a £50 voucher then you will lose out on £25 for a £25 flight. Similarly if you book a £51 flight you are left to pay £1 or £13 for the use of your debit card, useless.

on this occasion my flights totalled £24 return, my voucher totalled £30.
£5 was lost in purchasing the voucher, and £1 lost due to the cost of the flight being £1 below the value of the voucher.
So £6 for the use of a voucher rather than £12 for the use of my debit card.
Total saving £6, and there were no need to enter my debit card fee

So, my handy tip is.

If the total cost of your flight is £25/£50/ etc, and you only have a debit card. Then purchase a voucher which you will receive immediately or in your inbox later. This can later redeem it on your flight as a method of avoiding the card/admin fee and save yourself £7.

Generally it works better when the value of the voucher matches the cost of flight, or anything just below it without exceeding £11.

I think this advice ought to be used on this website, particularly when the above applies.

I think you have failed to mention a major advantage of this method. It becomes incredibly beneficial if you are making a group booking, considering the credit card charge is €6/£6 per passenger each way. See below example.

Imagine you are booking for 4 people. The total cost of flights, before credit card charges, comes to say €190. Credit card charges will amount to €48 (€6 per person each way), bringing the total to €238. Now you buy a €200 voucher and pay €5 for the doing so. (total €205). You then pay for the flights with the voucher. Yes, you do lose the difference between the voucher amount (€200) and the initial cost of flights (€190), but instead of paying €238 in total, you pay €205, a saving of €33.

I also find the voucher system useful for setting a limit. I like to fly Dublin to London Stansted return every few months, flying Dublin to Stansted on Friday evening and returning on the following Saturday evening (same airports). I am highly flexible on time and I have the following rule, I will go when I can get flights for no more than €55.00 in total (and not a cent more). The limit is calculated as a €50 voucher + the €5 purchase charge. If flights prices come to €49.99 + €12.00 credit card charges, totalling €61.99, I can purchase the flights for €55.00, saving up to €6.99.

My point is, a limit has to be set to something. You may as well set it to take advantage of the voucher system.

Hope you find this of interest.