I'm not a lawyer but I am involved in dealing with employment issues on a regular basis and unfortunately a 'considered opinion' is never given without sight of the relevant documentation, in this case the contract and the documentation from the HR people. You are doing the right thing in taking legal advice therefore. Personally, I'd feel that you have a good chance of proving that the HR documentation forms part of your contract:-
".....the employer, as an alternative to providing all the details in the statement, may use the statement to refer the employee to certain other documents containing the particulars, provided such documents are reasonably accessible to the employee in his/her employment."
As there are already statutory avenues open to you in order to address the matter yourself if necessary, you may not need to actually employ a lawyer and I can suggest 2 approaches:-
Call the Employment Rights Information Unit (details in above website) and/or ask to see a lawyer under the FLAC scheme as operated through the Citizens Information Centres and in certain other locations. Some Centres operate on an appointment-only basis, others are 'walk-in'. In either case be sure to bring your documentation with you.