I don't know if this helps, but I asked the same question on another forum & I got this reply:

If it's a radio broadcast that's being played and not a CD or other recording and the people listening are not being charged to do so and the broadcast doesn't substantially effect the prices paid (i.e. customers are not there for the music) then it's not a copyright infringement under the act.

EDIT: To save you reading it all here's the appropriate part of the act which I think exempts you from paying for a radio for your staff.
Please check the updates !

Copyright, Designs and Patents Act 1988

http://www.legislation.gov.uk/ukpga/1988/48/section/72

Section 72 Free public showing or playing of broadcast or cable programme -

(1) The showing or playing in public of a broadcast or cable programme to an audience who have not paid for admission to the place where the broadcast or programme is to be seen or heard does not infringe any copyright in—

(a) the broadcast or cable programme, or

(b) any sound recording or film included in it.

(2) The audience shall be treated as having paid for admission to a place if —

(a) they have paid for admission to a place of which that place forms part; or

(b) goods or services are supplied at that place (or a place of which it forms a part) — and

(i) at prices which are substantially attributable to the facilities afforded for seeing or hearing the broadcast or programme, or

(ii) at prices exceeding those usually charged there and which are partly attributable to those facilities.

(3) The following shall not be regarded as having paid for admission to a place —

(a) persons admitted as residents or inmates of the place;

(b) persons admitted as members of a club or society where the payment is only for membership of the club or society and the provision of facilities for seeing or hearing broadcasts or programmes is only incidental to the main purposes of the club or society.


Please remember that this is just one persons opinion/interpretation of the rule and may not necessarily be correct, but it stopped them pestering me.

Graham