The thing you must bear in mind is that you will have to backdate any formal arrangement because the Revenue will look into your arrangement. If you only have one client, then you will be deemed to be an employee, and therefore be charged like one. This could include your client having to pay NI contributions for you.

There could also be an issue with your current employer - most councils in the UK forbid their staff from working elsewhere, and definitely frown on them being given gifts.

I would recommend you consider forming a limited company, and registering for VAT. This makes life more complex, but also good when you can offset expenses and the VAT on them.

I would definitely consider contracting again, were the situation to arise again...

Regards
Simon