Sorry! IGI is a worldwide database put together by the Mormons (something to do with wanting to trace their non-mormon ancestors to convert them!) Anyway, its the basic genealogical tool and can be accessed free of charge on the web at www.familysearch.org. It's global in coverage, but in England they took down details of most parish registers - mainly baptisms but also a few marriages. Parish registers started in England in the 16th cent., and the mormons followed most through to about the 1850s/1860s. Just put in the name of the person you want to find (+ rough dates, if you have them) and every person baptised in England with that name comes up (or at least for the registers they've covered). This is most useful for the period pre-1837.After that you can get birth, marriage and death certificates from the Public Record Office (PRO).In your case, I would get your GFs birth certificate which will have your great grandmothers name in it. You should then be able to find their marriage cert. This will have your GGF's age, so you then can get his birth cert. You keep on going back like this as far as you can until 1837, then switch to the IGI. If you can find addresses for any of these people around the census time 1841,51,61,71,81 etc. (eg from certs), this will help because from 1851 the place of birth was noted in the census (this is also at the PRO).Getting the place of birth from the 1851 census is key because this will help you in getting the right person in the IGI. (If you get an old person in say the 1851 census it may take you to where the family came from before they moved to London.There was a big influx from 1800 onwards.If you can trace them to their locality, it will be a lot easier to track them back.) Sorry for the lengthy potted guide to English genealogy! There are several books you can get to take you through this.The PRO do a good one called Tracing Your Ancestors. (PRO also have an excellent website with a lot of help) There are a lot of other sources you can use: wills, apprenticeships, tax returns, poor law records.But I think what I described above is the basic building blocks. Good luck again!