You're not comparing the same stats. The original stat was growth rate compared to the rest of the country. Islam's overall growth rate has been fairly steady for decades, although admittedly it has slowed, but at a rate that could conceivably stop above Christianity, which your chart shows is decreasing about as rapidly as Islam is rising. I think it's reasonable to project that it may settle below Islam eventually. Realistically, there will be continued backlash by native English and that may temper immigration, though even if immigration stops, the birth rate of Muslims in the UK is still much higher than native population.

However - if we're including atheist then clearly that'll be the majority position.