Yes, £70,000 is a good salary for London (assuming you are not supporting other dependents). As others have stated, finding an affordable place to live will be the most difficult aspect and also present the most significant outlay.
The following website provides statistics for
weekly average rental prices for different sizes of properties (ranging from one room in a shared property, to studio flats to multi-room houses) - this should give you a rough idea of what your likely weekly outlay would be for an 'average' property of the type you would be looking for, and in the areas you might be likely to consider:
https://www.london.gov.uk/priorities...home/rents-map
It is probably worth cautioning that an 'average' property may be below the standard that you would ideally want to consider - but this would depend on so many different factors as to what you personally are looking for or would accept.