I think you need some education about London !
London is a HUGE city, there are people who live on the West of it who have probably never been to the East of it (and vice versa).
If you are going to work in London you probably need to live IN London (or spend a fortune in travel costs), so NOT Luton.
This map below shows London in white (What we call Greater London).
http://www.city.ac.uk/marcoms_media/images/map s/London%20Map.gif
Round London is a motorway called the M25, shown on the map in blue.
If you want to WORK in London you probably need to live INSIDE the M25 motorway.
As you can see from the map, Luton is WAY outside the M25 motoway.
Here is a map showing the greater London areas and their names.
http://www.mapsofworld.com/united-kingdom/maps /london-map.jpg
Those in the centre, like Westminster and Kensington are VERY expensive.
Ringed round them are cheaper areas that are just outside the centre, and fairly easy to commute from, like Fulham, Lambeth, Camden, Hackney etc. (although they can have very expensive parts).
As you get further out you get to suburbia, like Hillingdon and Epsom, which may be slighter cheaper but are now a long way out.
Getting from the EDGES of London to the CENTRE is fairly easy as all the tube trains gravitate towards the centre.
Getting ACROSS London, so from West to East or from North to South is NOT so easy as you have to go into the centre and come out again.
To be honest you are best finding out where you are going to WORK first and then work back from that to see where you want to LIVE