This is the section which applies to Governement Employees Pensions
http://www.hmrc.gov.uk/taxtreaties/in-force/spain-dtc.pdf
Article 18
GOVERNMENT SERVICE
1.
a) Salaries, wages and other similar remuneration paid by a Contracting State or a
political subdivision or a local authority thereof to an individual in respect of
services rendered to that State or subdivision or authority shall be taxable only in
that State.
b) However, such salaries, wages and other similar remuneration shall be taxable
only in the other Contracting State if the services are rendered in that State and
the individual is a resident of that State who:
- is a national of that State; or
(ii) did not become a resident of that State solely for the purpose of
rendering the services.
2.
a) Notwithstanding the provisions of paragraph 1, pensions and other similar
remuneration paid by, or out of funds created by, a Contracting State or a political
subdivision or a local authority thereof to an individual in respect of services
rendered to that State or subdivision or authority shall be taxable only in that
State.
b) However, such pensions and other similar remuneration shall be taxable only in
the other Contracting State if the individual is a resident of, and a national of, that
State.
3. The provisions of Articles 14, 15, 16 and 17 shall apply to salaries, wages,
pensions, and other similar remuneration in respect of services rendered in connection
with a business carried on by a Contracting State or a political subdivision or a local
authority thereof.