I do freelance work and charge a daily rate. This is based on 7 hours work per day. I usually include with my invoice, a breakdown of what tasks I did in those hours and on this document it states one day = 7 hours. I've never had anyone arguing!
Hello fruitstick, I suggest joining a internet forum specific to your profession. There are lots of societies/trade unions (for example society of proofreaders/NUJ for journalists and proofreaders) who have rates on their sites. If you are more TV and entertainment the trade union is www.bectu.org.uk.
I have a daily rate and an hour rate for my work. If you have a daily rate you could divide by 7 hours and get an hourly rate. Lunchhour is only an issue if you work inhouse as a freelancer, in which case you are paid a daily rate anyway.
Good information on going self-employed is on the Inland Revenue's site. They have a handy, downloadable guide.
If you are billing per hour you wouldn't include an unpaid lunchbreak anyway, surely, you'd be billing for the actual hours you spent working....
If you are self-employed you can more or less do what you like, no one can tell you to take breaks, so no you are not required to take one if you prefer to squeeze more work into one day that's up to you.
I bill per day, so I'm not sure I can be much help, but thought I'd post to say hello and good luck with your new venture. I'm fairly new to freelancing myself - been doing bits and pieces for a year now, alongside a one-day a week proper job. I'm not sure what the legal position is, and someone might come along more knowledgeable than me, but I think the whole point of being freelance (and indeed one of the definitions of it for tax purposes) is that you can do the work when and where you want. So if you want to work without a break from 8am to 8pm you can - though I must say my problem working from home is more making myself stop taking breaks...
When calculating your daily/hourly rate, remember that you have to add for holidays, sick leave and fallow periods, so don't base it slavishly on your salary.