wrote in message
I only ask because I thought they only had their police powers on railway
property and a few other transport related areas (but specifically NOT
roads).
However the other day I saw a BTP marked car pull over an elderly motorist
on
a main road.
Are they allowed to do this or should they have called the local plod to
do it for them? If they do have police powers outside their usual areas
does this now extend to anywhere in the country (given they're a
nationwide
force)?

Section 26 of the Anti-terrorism, crime and security Act 2001 says,

26. Sections 98 to 101 and Schedule 7 allow the British Transport Police
("BTP") to act outside their railways jurisdiction when asked to assist with
a specific incident by a constable from the local police force, the UKAEA
constabulary or a Ministry of Defence Police ("MDP") officer, and in an
emergency. The changes also give BTP officers certain powers available to
local police officers, including powers under the Terrorism Act 2000 and
powers to enter into mutual aid agreements with other forces.

Section 100 says,

100 Jurisdiction of transport police

(1) Where a member of the British Transport Police Force has
been requested by a constable of-

(a) the police force for any police area,
(b) the Ministry of Defence Police, or
(c) the United Kingdom Atomic Energy Authority Constabulary,
("the requesting force") to assist him in the execution of his
duties in relation to a particular incident, investigation or operation,
members of the British Transport Police Force have for the purposes of that
incident, investigation or operation the same powers and privileges as
constables of the requesting force.

(2) Members of the British Transport Police Force have in any
police area the same powers and privileges as constables of the police force
for that police area-

(a) in relation to persons whom they suspect on reasonable grounds
of having committed, being in the course of committing or being about to
commit an offence, or
(b) if they believe on reasonable grounds that they need those
powers and privileges in order to save life or to prevent or minimise
personal injury.
(3) But members of the British Transport Police Force have
powers and privileges by virtue of subsection (2) only if-

(a) they are in uniform or have with them documentary evidence that
they are members of that Force, and
(b) they believe on reasonable grounds that a power of a constable
which they would not have apart from that subsection ought to be exercised
and that, if it cannot be exercised until they secure the attendance of or a
request under subsection (1) by a constable who has it, the purpose for
which they believe it ought to be exercised will be frustrated or seriously
prejudiced.
(4) In this section-

"British Transport Police Force" means the constables appointed
under section 53 of the British Transport Commission Act 1949 (c. xxix).
Hope that helps.
Ian