A lot of wholesalers won't deal with you unless you are a registered business, as generally, wholesalers do not deal with the general public you have to be classed as
the trade.
A lot of wholesalers do however now deal with sole traders which is very easy to set yourself up as. Choose a business name, register as a business with HMRC, get a business bank account and your away.
If you are just doing this part time, go the sole trader route for a while and see how you get on. If you take it up full time, you may feel that registering a company is worth considering.
The implications of buying and selling are slightly different with each setup. As a sole trader you are responsible for the businesses debts and any troubles it may fall in to. In other words, the liability is at your door, personally. With a company however, the liability is shifted to the company itself, as it is a legal entity separate from yourself. If you choose a limited liability company, the liability would be held with the company and not (usually) affect you as an individual.
Hope that helps.