This is just a small section taken from the Copyright, Designs and Patents
Act 1988
1988 CHAPTER 48
Section 297A: Unauthorised decoders
297A.-(1) A person who makes, imports, sells or lets for hire, offers or exposes for sale or hire, or advertises for sale or hire, any unauthorised decoder shall be guilty of an offence and liable-
(a) on summary conviction, to imprisonment for a term not exceeding six months, or to a fine not exceeding the statutory maximum, or to both
(b) on conviction on indictment, to imprisonment for a term not exceeding ten years, or to a fine, or to both.
This section does not have effect in relation to any offence committed before the commencement of this section.
(2) It is a defence to any prosecution for an offence under this section for the defendant to prove that he did not know, and had no reasonable ground for knowing, that the decoder was an unauthorised decoder.
(3) In this section--
"apparatus" includes any device, component or electronic data;
"decoder" means any apparatus which is designed or adapted to enable (whether on its own or with any other apparatus) an encrypted transmission to be decoded;
"transmission" means any programme included in a broadcasting service which is provided from a place in the United Kingdom; and
"unauthorised", in relation to a decoder, means a decoder which will enable encrypted transmissions to be viewed in decoded form without payment of the fee (however imposed) which the person making the transmission, or on whose behalf it is made, charges for viewing those transmissions, or viewing any service of which they form part.
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So basically the section i have highlighted in BOLD says that you are innocent of any offence if YOU BELIEVE the system that you are using is legitimate.
If allowed i will post a link to the full copyright act, or just google it for more info.