The in/out of print status has no bearing on ownership of copyright for a work. Since you modified the question to be about the UK, the governing authority is the Intellectual Property Office. IANAL, this does not constitute legal advice.
The term of protection or duration of copyright varies depending on the type of copyright work. The term of protection in the UK for an original written (literary), theatrical (dramatic) musical or artistic work lasts for the life of the creator plus 70 years from the end of the year in which he/she died. ...
You should also note that. for copyright works originating outside the UK or another country of the European Economic Area (EEA), the term of protection may be shorter if it is shorter in the country of origin. There may also be variations in the term where a work was created before 1 January 1996.
Additional, since many works might be owned by a company, the IPO says:
An employer should keep careful records of which person(s) created the work for them which they own. The period of copyright protection may still be linked to the date of the death of the creator(s) - that is the employee(s).