The subject was discussed on BBC TV this morning and it appears it goes under the official title of 'Purdah Restrictions' which the Government imposes. On this occasion the mainstream media did as it was told. One of the items suppressed was reporting on Afghanistan. Indeed anything which might be seen to have a party political bias, which certainly would include many street demonstrations.
There was also this from the BBC.
"Government web activity was frozen during the general election campaign but now that the new coalition Lib Dem/Conservative government is taking shape it has exploded into frenetic life..."