Of course...
- It would be in or around London (but for the type of soil I'd have to do some research first)
- Burial is at April 9th, person dead since April 5th, but body is burned (died in a fire).
- Embalmed - no.
- Type of coffin - I think it would be plywood (have to do some research here, but in any case it would be some cheap material).
The thing is, I have NO idea how long it approximately takes (for average Western/Central European standards) until there is left nothing but bones.
I mean, if someone would tell me "between 2 and 5 years" or "between 10 and 15 years" that would already help a lot, as I have absolutely no clue.
You might want to look at
University of Tennessee Forensic Anthropology Center.
No one can tell you for sure, and two bodies in the same cemetery can have markedly different decomposition rates. Result is all you can get is a S.W.A.G. (scientific wild ass guess). London burials are probably somewhat close to the water table, if they go down the full six feet. But I doubt they go down a full six feet, because most of London involves graves that have seen multiple uses. Closer to the surface means you're probably going to get more variation in water, with soaking and drying both happening.
Being soaked tends to speed decomposition, being dry tends towards mummification. Repeated cycles tends to cause movement in the soil as the water drains down. This will help speed decomposition.
I don't know anything about the soil in London. Soil with high levels of acids tend to produce a lot of destruction to the body. Cold, damp soil tends to help in the production of adipocere, which slows decomposition. Body fat composition also helps in the production of adipocere, with the higher the fat content of the body, the more likely adipocere is to appear.
Decomposition for a buried body is about eight times as long as a body on the surface. (Water is about twice as long as a body on the surface.)
Lack of embalming will speed decomposition. However, you've got a burnt body, which preserves meat. Depending upon how badly burned the body is will be how much bodily fluids have exited the body. Lack of bodily fluids will delay decomposition. (Think jerked meat here.) Further, burning will impact the digestion system. Digestion, which continues after death, speeds decomposition.
Net result, and here's where the S.W.A.G. comes in, is my guess is that a body buried for two years with the conditions your describing would be significantly intact, with some level of adipocere, and some bone showing. Body would be easily recognized as human, and possibly maintain enough integrity in the face for some level of identification, at least identification consistent with her facial image after the fire.
But I wouldn't put any money down on this bet.
Best of luck,
Jim Clark-Dawe