Short answer is that if you are selling GOODS than no. There are no tax implications or reporting requirements in the US.
If you are selling services, than legally the US client is required to withhold 30% from your payment or get a filled out W8BEN from you claiming double taxation treaty benefit. The W8BEN is not difficult to fill out and stays on file with the client, it does not get submitted directly to the US government unless the client is asked to show proof that you can claim tax treaty benefit. There is a double taxation treaty in place between US and UK, so you are certainly eligible to claim tax treaty benefit but to do so you will need to apply for a US EIN number which takes about 10 minutes by submitting a form by fax to the IRS and has no cost and no impact on your US tax liabilities which remain 0 as an offshore non-US company.
If you're a UK Ltd company there are currently no tax implications in selling to the US.
You will need to have W-8BEN forms filled in (and it helps to have an EIN as well) and be ready to explain to your customers that W9's and so on are not relevant to you.
More info - Can I sell in the US without a SSN?
Generally speaking you won't have to collect Sales & Use Taxes or file Tax returns in any of the states in the United States, since you don't have physical presence in any State. This however can change at any time so I would suggest getting some professional help with this.
You will have to file an 1120-F to the IRS for any income your company makes from US sources.
The relevant legislation is VAT Act 1994, specifically paragraphs 7C(a) and 7C(b) of Schedule 5 which deal with “Electronically supplied services”.
This provides that VAT must be added to invoices where the customer is: