In June 2016, the Department for Health published a report on the Dangers of socket safety covers. This states that these should not be used in health or social care premises, and also not to be used in a home.
This message is repeated by the Royal Society for the Prevention of accidents (ROSPA)
"13-amp power sockets made to BS 1363 incorporate a shutter mechanism, which prevents inappropriate access to the live connectors. RoSPA therefore does not consider it necessary to recommend the use of socket covers."
(Source: www.rospa.com/home-safety/resources/policy-statements/electricity/)
The report from the Department of Health states "socket outlets have an interlocking shutter mechanism to stop the insertion of foreign material into the socket tubes. Socket covers are not constructed to any electrical or other safety standard. The pins on the socket covers may be larger than the socket tubes which can cause damage to the socket and defeat the safety design...the insertion of socket covers, can allow foreign objects to be inserted directly onto live parts within the socket, thus presenting a high risk of electric shock".
The full report can be found here:
http://www.careinspectorate.com/images/documents/News/EFA_2016_002_Final.pdf
For further information, please see here where a full explanatory video can be viewed
http://www.childalert.co.uk/article.php?articles_id=28