Copyright works, including phonograms (which are treated as such - see answer to question 1), and performers from other countries are protected as explained in answer to Question 1.
There is no single date to which the protection extends back since protection is always future protection but is given in respect of an existing copyright work or recording of a particular performance after it has qualified for protection in respect of any period which continues to subsist calculated from the date prior to qualification on which the work or recording of that performance was made, as required by TRIPS. Whether protection exists therefore depends upon whether the term, which would have applied to a particular work or recording of a performance had it always been protected, has expired.
Existing sound recordings made from at least as long ago as 1946 may be protected in the UK. The Copyright, Designs and Patents Act 1988 (which has been amended by the Duration of Copyright and Rights in Performances Regulations 1995) in paragraph 12 of Schedule 1 confirms the term of protection in the Copyright Act 1956 for sound recordings made before 1 June 1957 (i.e. the date of commencement of the 1956 Act). The 1956 Act in paragraph 11 of Schedule 7 gives a term of 50 years from making for sound recordings made before commencement of the Act. The 1995 Regulations may result in sound recordings made before 1946 being protected.
For literary, dramatic, musical and artistic works, under the 1995 Regulations mentioned above, protection may apply to existing works where the author died 70 years ago, i.e. in 1926. The 1988 Act, which the 1995 Regulations amend, confirmed the protection for works made before commencement of that Act in paragraph 12 of Schedule 1 by reference to Sections 2 and 3 of the 1956 Act, which should be read in the light of the transitional provisions in Schedule 7 of the 1956 Act with regard to works existing before commencement of the 1956 Act.
The Copyright (Application to Other Countries) Order 1993 as amended by the 1995 Order mentioned above gives effect to retroactive protection, subject, of course, to the term of protection having not already ceased, for all copyright works from all WTO countries. The 1995 Order does not restore any copyright because Article 18 of Berne does not require works that have already fallen into the public domain through expiry of copyright protection to be protected. Article 7 of the 1993 Order (amended by the 1995 Order) gives some protection to those who have or may be about to use a work newly protected by copyright. Article 7 allows the continued doing of certain acts unless the copyright owner pays compensation as settled by arbitration in the absence of agreement. How long the Act can be continued would depend on whether the Act fell within the scope of the Article. It would ultimately be for the courts to decide whether this is the case in any particular circumstances.
As far as performers rights are concerned, the 1995 Order mentioned above in reply to Question 1 grants reciprocal protection, i.e. the same as that applying under Part II of the Copyright, Designs and Patents Act 1988 to UK performers (except where there are limitations on this reciprocity as is indicated in the relevant Order). TRIPS Article 14.6 requires Article 18 of Berne to extend only to those rights of performers in sound recordings granted by TRIPS. By definition, the only right relevant here is the right to authorise the reproduction of a fixation of a performance. Section 180(3) in Part II of the 1988 Act ensures that insofar as rights in recordings are concerned, those rights apply after qualification to recordings of performances made prior to qualification except that no act carried out in relation to such a recording either prior to qualification, or after qualification but in pursuance of arrangements made before qualification, can be an infringement of rights arising after qualification. As with copyright, the extent to which existing performances are protected depends on whether the term of protection, had the performance always been protected, has already expired.