No they aren't.

 http://www.acpo.police.uk/NCDE/FreedomOfInformation.aspx

The Freedom of Information Act allows for information on an organisation to be accessed by anyone.

"If you ask for information about yourself, then your request will be handled under the Data Protection Act."
 http://www.direct.gov.uk/en/Governmentcitizensandrights/Yourrightsandresponsibilities/DG_4003239

The Data Protection Act 1998 covers information held about an individual which can be accessed by that individual. There is no get out clause for the NPOIU.

People are always mixing up these two separate pieces of legislation. Go to following link for more clarity.

 http://www.ico.gov.uk/

The NPOIU IS covered by the Data Protection Act, I have used it myself.

The NCDE, NDET and NPIOU do respond to Data Protection Act requests. NETCU are at Cambridgeshire police HQ HUntingdon. The address given (and confirmed with a visit last month) is 10 Victoria, London next to New Scotland Yard. They are based on the 7th Floor according to the address given by ACC Anton Setchell who responded to my request (all 24 pages of it). I think that they have come to need a whole floor in an office block to deal with the 2000 activists they have on a database there.
Demo?

Just to clarify. In your comment you say NETCU is based in Huntingdon.
You then say

'The address given (and confirmed with a visit last month) is 10 Victoria, London next to New Scotland Yard'.

Do you mean NETCU or NPOIU, and which did you do a Subject Access Request to?
Please put up the full address and any contact numbers, email etc, let's see if we can get 2000 requests for info!

Sorry didn't explain it well.
NETCU are at Huntingdon.
NPIOU and NDET (National Domestic Extremism Team) are thought to be at the same address as the NCDE (National coordinator Domestic Extremism, ACPO Terrorism and Allied Matters Business Area) which is at 10 Victoria Street, London, SW1HONN.
You can contact them via ACPO just ask to be put through, someone else has kindly supplied their website address (where I got their phone number) in a previous comment. I once phoned and a DC from NDET answered, so I am sure that they would be only too happy to answer any queries.
Regarding the Data Protection Act you can apply for information they may hold on you but very unwise if you are not sure whether or not they know about you and wish to remain anonymous as you will need to supply name address and photo. Speaking for myself my file is 24 pages long with an average of 15 entries per page littered with inaccuracies, says I attended demos which I was nowhere near, is full of comments/posts I have made on Indymedia and calls fox hunts "drag hunts". Anyone applying will only get back some of the information held, anything regarding another person or under investigation will not be forthcoming.
To ask the NCDE for info held by NPIOU on each of us especially concerning that supplied by infiltrators and informants may be something worth doing. Legal action can then be taken if they refuse to supply data which they are obliged to by the DPA.

You can politely contact NCDE,NPIOU, NDET via ACPO 0207 84 8950 (from their site). They are on the first floor of 10 Victoria Street according to the site. The building ( a large office block) has no signs indicating police or any company logo, just says "10 Victoria".
Again be cautious of being traced if you wish to stay off their radar.
Maybe it is time to put some energy into curbing the political police units who have been active in screwing over activists for the last few decades. At the end of the day the earth is dying, billions of animals are being slaughtered, humans are starving to death and being mercilessly oppressed, the police are through these units trying to stop us doing anything, literally anything to curb these atrocities. I think that much time has been spent discussing a certain undercover PC but we need a strategy about what to do with those who are probably at this very moment sat around some table quaffing donuts and deciding on how to hit us hard after what must have been highly embarrassing for them. They will respond in the press with some shitty story sooner or later.