Does anyone have experience with any other private London guides other than those recommended in Rick's London book? If so let me know your opinion and what cost for full day.
I haven't ever used a private London guide. I have taken various guided walks and other excursions over the years and if it is run by an official "Blue Badge Guide" you are pretty much guaranteed a knowledgeable and efficient person.
Here is their website.
http://www.britainsbestguides.org/tour-ideas/
I would highly recommend London Walks which are in groups but take you to either quirky corners of the city or shed new light on some of the most famous sites.
If you do engage a guide it would be a good plan to know what you want to see that you couldn't do on your own. London is a big place and it would be very difficult to have a dull day wandering under your own steam. The locals speak English and public transport is good if not cheap.