On 2 April 2015 the UK will complete the move from quadrantal to semi circular cruising levels. This change affects pilots flying under instrument flight rules outside controlled airspace below flight level195, but higher than 3,000ft above mean sea level, as semicircular cruising levels have been used in controlled airspace for many years. The timescale for this change has been extended to allow a safe transition to the new arrangements.
Update on introduction of Standardised European Rules of the Air
Am not sure but would suspect the 3,000 ft amsl refers to the general TA outside CAS in the UK - if operating below a TMA the TA is appropriate to the controlling aerodrome. (6,000 ft for London?)