We have had a Dualit toaster for many (5 or so) years now. We have a 4-slice model, but they make others.

One of the good things about these is that they are made so you can easily swap out the elements when (if) one burns out. We have not had to do this yet.

I will find out exactly what model we have, and post back here.

Update

Our Dualit is a "4SL GB" highly recommended.

We have had a Dualit toaster for the past 5 or 6 years, and to this day, it works perfectly. My parents have had their Dualit toaster for at least 15 years, and it still works perfectly, too. These machines are manually-operated with levers (to move the bread up or into the toaster slots--it doesn't pop up with a spring) switches (to choose whether you have one or more of the slots heating) and dials (the clockwork timer to decide how long you want the elements to remain on), so there is nothing to go wrong, digitally. And if the heating element fails (something I've never heard of it doing), they are easily replaceable. The toaster we own is a 2-slice unit. You can also get them in 4-slice units, and you can purchase a basket for sandwich making that fits into the nice, wide slots for the toast slices. We have this sandwich basket, and use it often.

The Dualit isn't a cheap toaster, but it's well worth the investment. When our last "normal" toaster quit several years ago, my wife refused to purchase another until we could afford the Dualit. While they normally ran about $200 for the 2-slot unit, she found one on clearance in Kitchenkaboodle, and snatched up the last one they had. We've never looked back, and we've never regretted our purchase. The only thing my wife says she'd change is that, if it had been available on clearance, she would have purchased a red one. As it is, ours is dark blue. It still looks great!

Beware of look-alike imitations! If it's got spring-loaded slots, it ain't a Dualit!

Dualits are good and easily repaired - that's why commercial outfits and institutions use them. However, most small appliance manufacturers will say that their goods are expected to have a three year lifespan. So your goal of a 20 year toaster might be a tad optimistic. If you are able to access it, and are in the UK, Which? (UK version of consumer reports) has a good list of small appliance brands and those that tend to outlast the rest. Dualit got a good review if I recall.