The BARQA GCP Committee answered a similar question on 6th April 2010 (available on the BARQA website):--

From a legal perspective, since the UK Statutory Instrument 2004 No. 1031 cites the 1996 version then there is an expectation that this one would be referenced. This is also the version cited by the 2005/28/EC European Directive Article 3. It is understandable that the WMA expect only the latest version to be followed and from general feedback it appears the MHRA are taking a pragmatic approach. Many companies are adapting procedures to follow certain elements of the latest version of the DoH (e.g. allowing 'appropriately qualified’ individuals to take consent).
The MHRA answered a similar question at the GCP Consultative Committee 29 May 2009:-
“The GCP Directive stated that the Declaration of Helsinki 1996 was the standard for GCP. The Directive did not state that later versions would be automatically adopted by Europe.
The Commission has in the past commented that Europe cannot be legally bound to documents over which it has no control. Hence, fixing the version of the Declaration of Helsinki to be followed is consistent with the Commissions previously stated view. However, the UK was more flexible in its transposition of the GCP Directive.
In Schedule 1, part 2 – the ‘Conditions and principles of GCP…‘, point 6, states that Clinical Trials shall be conducted in accordance with the principles of the Declaration of Helsinki. We interpret this to be the spirit of the 1996 version. So long as later versions do not conflict in any practical and significant way with the 1996 version, there is probably no harm done by clinical trials organisations stating that later versions are being followed.”

Bear in mind that the MHRA do primarily inspect against the UK legislation and where there are differences between the DoH and the Statutory Instruments then the latter will always take precedence.

As an aside, it is interesting to note that last year the US FDA removed the requirement for ‘foreign studies not conducted under an IND’ to be conducted in accordance with the DoH so long as they are conducted in accordance with GCP (Federal Register vol 73, No. 82, 28 April 2008).

NEW Addition- Also the new EU proposed draft Clinical Trial Regulation now quotes DoH 2008.