I asked about secretary for _Limited Company_. Not for advice what I should do.
I'm going to be a freelancer/contractor and if you're working _only_ for someone 40h/week for few weeks as sole-trader (self-employed) you should be employed by that company. Simple British law.
I'm going to work for one of the most famous recruitment agency in London. LTD company is a must. I'll pay for accountant so everything will be filled on time.