There have been a number of attempts to estimate these values, knowing that it is very challenging to count things that didn't happen.
A good summary of available statistics is given in The Population History of England, 1541-1871 by E. A. Wrigley and R. S. Schofield (2010).
There are chapters and chapters of statistics and commentary on this subject, so I'll just include a couple of interesting figures here.
In particular, see Table 5.23 (p 135):
If we just look at the figures for the decade 1811-21, for example, we can calculate that:
- about 67% of births were baptised in the Church of England
- about 10% of births were baptised in non-conformist churches, or baptised later in life. Figures given elsewhere (see table 4.2) further break this down and estimate that about 5-6% of all baptisms were non-conformist baptisms (excluding Quakers).
- about 22% of births were not baptised
A more graphical representation of the above data is given in Figure 5.1. Per 1000 births, you can see how the percentage of Anglican baptisms vs nonconformist baptisms vs unregistered births changed during this period:
I would stress that only estimates are possible and that other sources may give different figures. Also note that non-conformity was rapidly growing during the early 19th century, so the figures from 1800 do differ significantly from 1830.