rob, you don't live in London do you? are you familiar with this route at all?
The instructions my brother-in-law has given me..
The first one is a map of the Underground network, this is to give you an indication of how the Underground (subway) system works, you will need to use it to go from either Paddington Station to Liverpool St Station or from Hammersmith to Liverpool St depending how much money you can afford. Always think about $2.50 for evry £1.00
www.tfl.gov.uk/tfl/pdfdocs/colourmap.pdf This second link will be the easiest and fastest way for you to get across London. In the arrivals lounge of Heathrow, you will see signs pointing down to the rail and Underground. This link suggests that you catch the Heathrow Express to Paddington Station then transfer onto the Hammersmith and City line (pink Underground, see map) and then onward to Liverpool St. The prices for the Heathrow Express are in the 3rd link. You will be able to get directions in Paddington to the Hammersmith and City line.
http://journeyplanner.tfl.gov.uk/user/XSLT_TRIP_REQUEST2 www.heathrowexpress.com/index.asp?SID={04E2FFA9-0DE9-43D9-9C5E-9B4DE6573394} The other option for you (longer and cheaper) is to catch the Underground (Tube) on the Piccadilly Line from Heathrow to Hammersmith and then go out the station and accross the road to the Hammersmith and City line and then onwards from there. Once again you can get directions. All trains run very frequently as well.
www.tfl.gov.uk/tube/downloads/pdf/maps/piccadilly.pdfwww.tfl.gov.uk/tube/downloads/pdf/maps/hammersmithandcity.pdf www.tfl.gov.uk/tube/ See how you go with what you want to do, it will be pretty crazy for you both. When you get to Liverpool St look for the counter for the Stanstead Express. Get an open return, the last link is their homepage, youll be looking at about$60 or £25 for your tickets. That one is pretty straight forward.
www.stanstedexpress.com/ I do need to stress to you that it is very important that you make it to Stanstead in plenty of time, you do not want to miss your flight, you may not get another and if you do, you probably wont be able to afford it. You will be very tired after the trip when getting into Heathrow and it will be quite daunting, stressful (hopefully not) and tiring getting across London.