MI5 currently employs around 4,400 people.
At any time, several hundred staff may work in MI5 on secondment or attachment from other government departments and agencies.
Staff roles cover a number of areas including investigations, translation, data analysis, technology, surveillance, communications, information management, protective security, administration, building services and catering.
MI5’s headquarters are at Thames House, a Grade II listed building situated only a few hundred yards from the Houses of Parliament in London. We also have several regional offices and a headquarters in Northern Ireland.
MI5 operates under the statutory authority of the Home Secretary, but it is not part of the Home Office .
The head of MI5 is the Director General (DG), currently Ken McCallum. He is supported by the Deputy Director General (DDG), Director General Capability (DGC) and Director General Strategy (DGS).
The Deputy and Assistant Directors General share responsibility for MI5’s capabilities and functions, which are organised across ten branches.
The legal branch, which supports all parts of MI5’s work, reports directly to the Director General.
The Joint Terrorism Analysis Centre (JTAC) and Centre for the Protection of National Infrastructure (CPNI) are also accountable to the Director General, although both are self-standing organisations staffed by multiple government departments.
MI5's budget is paid from the Single Intelligence Account (SIA) which also provides funding for the Secret Intelligence Service (SIS) and Government Communications Headquarters (GCHQ).
The SIA's budget is decided by Ministers through the Spending Review. This process helps Ministers decide how much to spend on security and intelligence, in line with decisions on overall government spending.
The SIA was provided a settlement of £2.4bn in 2018-19. The agencies are also able to bid for additional resources from the Joint Security Fund, which is shared with the Foreign Office, Ministry of Defence and Departments for International Development. The breakdowns for the individual agencies are not published for security reasons.
At any one time the UK faces a range of covert threats to its security and MI5 has only finite resources with which to counter them. We prioritise the threats and allocate resources accordingly, taking into account the national intelligence priorities set by the Joint Intelligence Committee (JIC) .While we don't publish MI5's share of the SIA budget, the diagram below gives an overview of how we use our resources.
Allocation of resources by core business, 2018/19:
We are subject to close budgetary scrutiny and challenging efficiency targets. Although we have to operate in secret, we have to account for the money we spend in the same way as other public sector organisations and our accounts are audited by the National Audit Office (NAO). NAO staff have access to relevant MI5 records for this purpose. In addition, our expenditure and resource allocations are scrutinised by the Intelligence and Security Committee (ISC). The ISC's annual reports provide further details of the agencies' funding and expenditure.
The DG, DDG, DGC and DGS, Directors and the Legal Advisor constitute the Management Board and meet regularly to consider policy and strategic issues. The Board decides how the priorities and organisation of MI5 should adapt to reflect changes to the threats. Its decisions are subject to the external validation processes described in how MI5 is governed.
In 2011, His Royal Highness The Prince of Wales agreed to become Royal Patron of the Intelligence Services (MI5, SIS and GCHQ).