Now is a very good time to check your Sky box. A swathe of older set-top devices are now sadly out of date and have already lost access to many BBC and ITV services. Now there's another nail in the coffin with Channel 4 also confirming that its content will no longer be available on some Sky gadgets. The change affects those still using Standard Definition (SD) gadgets that are't able to tune into High Definition content.

SD signals have been slowly switched off over the past few months in a bid to free up some much-needed space and now Channel 4 and a number of its other services are joining the HD-only party.

Confirming the news about its SD channel closures a Channel 4 spokesperson told The Sun: "We are changing the technology we use to broadcast our channels to Sky and Freesat households – ensuring we are delivering the highest quality HD viewing experience to all, and, opening up the potential for new services in the future,"

"With Sky customers being encouraged to move to HD boxes, this will affect only a very small number of viewers.

"This follows similar moves by ITV and Sky earlier this year. All our channels, along with a wide range of on-demand content, are also available on Channel 4 streaming via smart TVs, mobile, tablets and PC’s.

"Sky customers are able to upgrade to new equipment at no cost.

"There are no changes on Freeview and Virgin Media, plus, satellite viewers with HD boxes are unaffected."

Sky has been alerting SD users for some time that they need to upgrade to the much more advanced Sky Q platform to keep watching the full list of channels.

This upgrade is available totally free of charge and also adds new features such as content streaming, improved recording and better personalisation.

"You can upgrade to Sky Q at no extra cost. Upgrade online or call 0333 759 5121 - we'd advise doing this as soon as possible to avoid long wait times," Sky explained.

"Your new box will be installed by one of our engineers on a date that suits you. You can then access all of the Sky channels in your Sky TV package."

To find out if your Sky box is affected you can simply select channel 101 on your remote. If you see BBC One HD, you're not affected. If you see BBC One in SD, you are and you'll need to upgrade your Sky box.

You can also check the model number via your remote.

Just press Services then press 4 then 5

The affected boxes are:

Digibox

4F01 to 4F08 (Amstrad) ¶ 4E01 to 4E05 (Grundig) • 9F01 to 9F08 and 9F0A (Pace) • 0F01 to 0F05 (Panasonic) • 4E06 to 4E08 (Thomson)

Sky+

4F2001 to 4F2006 (Amstrad) • 4F2101 to 4F2118 and 9F2101 to 9F2137 (Amstrad or Pace) • 9F2001 to 9F2024, PVR2, 9F2201 to 9F2235, 9F2301 to 9F2339 (Pace) • 4E2101 to 4E2141 (Thomson)