Here is a PDF info-sheet, plus photos, about the very handy magnetic strip secondary glazing which I have on my windows.
I also in 2015 made a short (9-minute) video, in which I and a colleague tell you about its advantages and show you how it's installed.
As at February 2023 it's had 180,000 hits, and hundreds of useful comments; please do watch it!
Magnetic strip secondary glazing is inexpensive and easy to do; it's unobtrusive (good for conservation zones and listed buildings) and very long-lasting; it does the same job as expensive secondary glazing systems.
I achieved brief fame in 2014 in a piece in a national newspaper, talking about this very useful energy-saving measure.
Click on photo for larger image
Also useful for fly-screens: You can also make fly-screens for use on your windows when the acrylic isn't on them. You can buy a self-assembly window fly-screen* and add magnetic strip on the back of the frame. You can even have a fly-screen over part of the window, for example just one of the casements. The screen is so light that it only needs to have fixing (magnetic strip to steel strip) on a couple of sides; and unlike when using the acrylic, for a simple fly-screen you're not needing a close seal on all edges.
*See this fly-screen system that I bought a few years ago. It comes with instructions, and you follow them to the point where you have a completed frame, and then treat it like an acrylic panel re adding the magnetic and steel strips.