TP-Link Smart Plug WiFi Outlet (Tapo P100) £9.99 @ Amazon
Apply the £3 voucher on the page for this price.
New smaller smart plug from TP-Link (see customer photos for size comparison). This also uses a different app to the Kasa range.
Argos have the Kasa version on 3 for £30.
* Please note that all prices are correct at the time of posting. However prices can vary quickly and significantly without warning.