Thanks for your question.
It's actually very simple to register a company at Companies House, once it has been registered the company is in existence albeit that it may not be trading because you are not actively doing business. You can register online by using the Companies House website:-
It's similarly uncomplicated to set up a LLP and you can see the link on the above site for Limited Liability Partnership. I believe you can set one up by submitting two forms to Companies House. Again, once registered the firm will be "in existence".
It's perfectly fine to form a company and run it in your spare time, provided your business needs do not dictate that full time staff are required.
The key, I suppose, if you are both going to be the main shareholders/partners in the business is to be clear about your responsibilities, duties, what happens to profits or debts incurred, equity brought in or taken out by you, and what happens in the event of dispute or deadlock on issues. These issues can be dealt with in the case of a company by a shareholder agreement executed by you both or in the case of a partnership a partnership agreement executed by both.
Both documents would set out specific clauses on the above mentioned points and would be a binding contract between you both. I wouldn't bother paying a solicitor to form the company/partnership because it's very simple for you to do on your own but I would instruct a solicitor to draft such an agreement for you, particularly if you think you will either make significant money from the enterprise or anticipate working full time in the future then I would advise you to seek advice from a solicitor to get one drafted.
You can find solicitors in your area using the following Law Society search engine, just put in your postcode and select "business services":-
Get them to do it for a fixed fee and then get your money's worth by pestering them on the phone or by email on the detail, it pays to be clear from the start. Have an written idea about what you're going to ask to be included in the agreement on the above points before you go in there.
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