Wow!
First of all, thank you, to all who commented and gave advice, there are a lot of points that I already knew in the back of my mind, but it is 100% better when several people confirm.
I have designed a website, I have business plans already written, albeit they need updating and reviewing, I never fixed on a name but that's trivial for the paperwork and website / logo.
I guess with regards to repairs, I am frequently repairing electronic gadgets and computers for friends and family and friends of, I guess the advice I can take is not to go seeking repair work, but not turn it down if I can and it comes my way.
Suppliers, yes, I can see how that can get messy, however, due to the nature of the work I do, I am in contact with a lot of decent suppliers, but yes, you still have to be careful who you go with just in case they mention to someone else and things escalate where I don't want them to.
I have family who do book keeping and family who are sole traders and they are willing to help, I have family who are home all day willing to take delivery of goods for me, I am very lucky in these respects, I can get a fully qualified accountant to do the necessary for a bit less than the £1k advised figure.
I am under no false illusion that I will forever be able to manage both, I wouldn't want to, I would quite like to start small, and grow, rather than try and "explode" onto the scene, advertising would be difficult in any case whilst still employed.
With regards to the employer, I have a full copy of my contract, which I have gone over by myself and with several others looking for anything that will potentially stand in my way.
There is no clause in there that states an form of IP will be retained whilst being employed, the contract was not written by the HR manager but in fact by the QA manager, over the many years I have been at this company I have seen people come and go and start their own businesses in similar fields as it turns out, but not one of them has had any comeback, one employee asked about going P/T to run a business and the MD said no, either stay employed or go fully on your own, so this is one reason I don't want to tell him, as it would then put me in the spotlight.
The only clause written is that "I will not run a competing business within a 25 mile radius whilst being employed by the company", that is it.
I can see the point about everything costing 2 x what is expected (money and time wise), and I am aware that I will need some kind of liability insurance, I have had a look at this and it seems that for £150 a year you can get fairly decent cover for what I would need.
I was going for the do whatever comes my way approach, but wanted to double check as sometimes there are ways that worked better for others, so it's pro's and con's for both as each situation is different.
I read a business case study where a ltd company director was working for a company, and his own company grew so rapidly that he had to employ staff, and when he handed his notice in he already had 50 or so people working for him, crazy!
One thought that led me to the sole trader vs ltd company route question was that I don't know if it is such an issue these days, but some suppliers or customers would deal with you unless you were ltd, apart from the up front vs 30 days on account benefit for a ltd company you have now I am not sure there is much in the way of difference from that point of view.