A Muslim majority in the UK? Statistical analysis.

There's such a lot of nonsense spoken on this subject that I thought I would try to apply some statistical rationality to it (it's a long post!).

Current Population
The 2011 Census recorded 2.79m (4.8% of pop) self-reported Muslims in the UK. I cannot find any hard-and-fast statistics for inflows since, however most reasonable on-line anecdotal evidence assumes at least half of all new arrivals are Muslims. Extrapolating from figures in my "Statistics on Immigration" thread, which showed 671k new entrants and a guesstimate of 640k illegal immigrants (also counting 50% as Muslim) that would mean a further 335k and 320k = 655k equalling 3.45m.

On that 2011 Census, 7.2% of the respondents (4.55m) kept their religion to themselves. I cannot see any reason why Muslims would be any more or less likely to do so, so lets assume that the national average of Muslims - 4.8% - of that 4.55m are also Muslims. That would mean another 218k giving the UK a credible Muslim population of 3.67m (5.7% of pop) as we stand.

Birth Rate
The Washington, US, based Pew Research Center is probably the world's most reliable source for demographic analysis, so I will be using their statistics.

Currently, non-Muslims in the UK have a birth-rate of 1.8 children per couple, which is not enough to self-generate (that normally falls between 2.0 - 2.1). Pew feel this is likely to stay about the same over the next 100 years, as it becomes the norm for Western families to be smaller. The non-Muslim population will therefore gently decline.

The Muslim birth-rate is 3.0 children which predicates a rapid expansion in that population. However, this rate is also in decline long-term as it heads more towards UK norms. Pew estimates a fall to 2.5 children by around 2030, although that is still considerably expansionary.

Due to recent immigration and a recent history of higher birth-rates there is also now a demographic 'bulge' of younger Muslims compared to the non-Muslim population. This will provide a one-off 'hit' of extra children over the next 20 years.

It is statistically relevant to mention that new immigrants are certain to conform to birth-rates of their home countries initially, so the first generation will always produce a much greater amount of children. As these children have children, the birth-rate will drop accordingly.

Other Factors
There are simply a huge amount of other factors that can effect numbers. Immigration will be the key one, but also numbers converting to/leaving Islam, inter-faith marriages (these are very low at present in the Islamic community) and a general secularising effect of Western European countries. Again, the latter is not happening at the moment with Muslims still very religious (78% regarded their religion as 'very important' - NOP, 2006).

Predictions
Based on the 2011 Census, and assuming immigration does not change significantly, Pew gives a figure of 5.52 million British Muslims by 2030, some 8.2% of an expanded 67.3m UK population. This is an increase of 98% over 19 years, against a population increase of about 6.1%.

I am therefore setting a benchmark 100% increase over 20 years on a 6.1% rising population which approximates very closely with the above figures.  I'm also basing predictions on my late 2014 (I'll call them 2015 for neatness) figures of 3.67 million - 5.7% of a 64.1m UK population.

Table 1. Assuming a 100% Muslim population increase over 20 years as forecast by Pew. (Year/Muslim pop/Total pop/Muslim percentage of pop)

2035 7.3m 68.0m 10.7%
2055 14.7m 72.2m 20.4%
2075 29.4m 76.6m 38.5%
2095 58.7m 81.2m 72.5%

This would see Muslims become a majority (i.e. 50.01% of population) by 2082.

Table 2. Downgrading to a more modest 75% Muslim population increase over 20 years. (Year/Muslim pop/Total pop/Muslim percentage of pop)

2035 6.4m 68.0m 9.4%
2055 11.2m 72.2m 15.6%
2075 19.7m 76.6m 25.7%
2095 34.4m 81.2m 42.4%
2115 60.2M 86.2m 69.8%

Muslims would become a majority in this case by 2101.

Table 3. Downgrading again to an even more modest 50% Muslim population increase over 20 years. (Year/Muslim pop/Total pop/Muslim percentage of pop)

2035 5.51m 68.0m 8.1%
2055 8.3m 72.2m 11.5%
2075 12.4m 76.6m 16.2%
2095 18.6m 81.2m 22.9%
2115 27.9M 86.2M 32.3%
2135 41.8M 91.4M 45.7%
2155 62.7M 97.0M 64.6%

Muslims would become a majority in this case by 2140.

Conclusions
I like the Table 2 prediction. Table 1 should technically be the most accurate, being bang in line with Pew's forecasts and actually being LESS than the 69% rate of Muslim increase from 2001-2011. However this whole exercise is based on the dubious science of extrapolation (!) and it just doesn't feel right to me. Repeated 100% increases hardly ever occur and surely have an upper limit.

I would be staggered if Table 3's prediction is correct. It would probably need some combination of a massive drop-off in birth-rates, a surge in inter-marrying, considerable secularisation and an end to immigration. There is absolutely no sign of any of those occurring as we stand.

Table 2 looks and feels right to me.  I believe it's statistically credible and moderates the Pew figures based on a presumed impact of some or all of the factors mentioned above. I would call Britain being a Muslim majority country shortly after 2100 i.e. slightly less than 100 years time.

As mentioned before, these stats are based on forecasting and extrapolating, and many factors can change as the years go by. Please feel free to tear this apart on a mathematical basis!  I don't claim to be a demographer or scientist, I've simply tried to apply a bit of logic to a very hard to quantify subject.