In this connection it's sometimes suggested that the duty to have such a notice of contact details for legal purposes is a German peculiarity. It fits so well into the image of German bureaucracy. But not at all - it's an EU requirement, and has been implemented in the UK too.
There's a post (in German) on the terrors of the UK equivalent today by Max-Lion Keller in it-recht kanzlei.
This is about online shops, so I don't think translators have to have it. Nor do German online businesses, unless they have a branch in the UK - then they can use their friendly German Impressum.
But if they do have a UK branch, they are subject to The Electronic Commerce (EC Directive) Regulations 2002. Here you go:
General information to be provided by a person providing an information society service
6.—(1) A person providing an information society service shall make available to the recipient of the service and any relevant enforcement authority, in a form and manner which is easily, directly and permanently accessible, the following information—
(a) the name of the service provider;
(b) the geographic address at which the service provider is established;
(c) the details of the service provider, including his electronic mail address, which make it possible to contact him rapidly and communicate with him in a direct and effective manner;
(d) where the service provider is registered in a trade or similar register available to the public, details of the register in which the service provider is entered and his registration number, or equivalent means of identification in that register;
(e) where the provision of the service is subject to an authorisation scheme, the particulars of the relevant supervisory authority;
(f) where the service provider exercises a regulated profession—
(i) the details of any professional body or similar institution with which the service provider is registered;
(ii) his professional title and the member State where that title has been granted;
(iii) a reference to the professional rules applicable to the service provider in the member State of establishment and the means to access them; and
(g) where the service provider undertakes an activity that is subject to value added tax, the identification number referred to in Article 22(1) of the sixth Council Directive 77/388/EEC of 17 May 1977 on the harmonisation of the laws of the member States relating to turnover taxes—Common system of value added tax: uniform basis of assessment(1).
(2) Where a person providing an information society service refers to prices, these shall be indicated clearly and unambiguously and, in particular, shall indicate whether they are inclusive of tax and delivery costs.
It's pretty draconian. Of course, we do not find any term there equivalent to Impressum.
Pinsent Masons have a guide here.