This is what Companies House says
On all of its business letters, order forms or any of the company’s web sites, the company must show in legible lettering –
its place of registration
its registered office address
and if it is being wound up, that fact,
According to Contractor UK. The problem here is that there is no date on the article so I'm not sure how current this is.
At a glance, the legal duties now facing directors of limited liability partnerships, limited companies and all UK companies are as follows:
The requirement is to show, whether in hard copy, electronic, or any other form, the company's name on:
all the company's business letters, order forms;
all its notices and other official publications;
all bills of exchange, promissory notes, endorsements, cheques and orders for money or goods purporting to be signed by, or on behalf of, the company;
all its bills of parcels, invoices, receipts and letters of credit
on all its websites
And also, on all its business letters, order forms, or any of its websites the following information:
-its place of registration
-its registered office address
-and if it is being wound up
More details about the Companies Regulations 2006 can be found via the Companies House webpage, with an onwards link to the regulations.
Another article on The Register from 2006 says this
Information that must be on your website
The following is the minimum information that must be on any company's website (from OUT-LAW's guide, The UK's Ecommerce Regulations).
The name, geographic address and email address of the service provider. The name of the organisation with which the customer is contracting must be given. This might differ from the trading name. Any such difference should be explained – e.g. "XYZ.com is the trading name of XYZ Enterprises Limited."
It is not sufficient to include a 'contact us' form without also providing an email address and geographic address somewhere easily accessible on the site. A PO Box is unlikely to suffice as a geographic address; but a registered office address would. If the business is a company, the registered office address must be included.
If a company, the company's registration number should be given and, under the Companies Act, the place of registation should be stated (e.g. "XYZ Enterprises Limited is a company registered in England and Wales with company number 1234567")
If the business is a member of a trade or professional association, membership details, including any registration number, should be provided.
If the business has a VAT number, it should be stated – even if the website is not being used for e-commerce transactions.
Prices on the website must be clear and unambiguous. Also, state whether prices are inclusive of tax and delivery costs.
Finally, do not forget the Distance Selling Regulations which contain other information requirements for online businesses that sell to consumers (B2C, as opposed to B2B, sales). For details of these requirements, see our guide, The Distance Selling Regulations - An Overview.
For help with email notices, such as disclaimers, see OUT-LAW's guide on Email notices.