High Remain vote in West Hampstead, but turnout only average

Camden has released more details of the Brexit vote. The results are not strictly ward based (the count was organised in this way for reasons of accuracy) as postal votes were allocated randomly and evenly per ward. With that caveat, the percentage vote in favour of remain in the the local wards was:

Hampstead Town 79.72%
Fortune Green 79.71% (just pipped by Hampstead)
Frog & Fitz 79.18%
West Hampstead 78.43%
Swiss Cottage 77.79%
Highgate 77.06% (said to have been highest, but wasn’t)
Kilburn 70.20%

However, the results also reveal a surprise on turnout. Despite photographs of queues at West Hampstead Library polling station making the national press, turnout in Camden overall was 65.5%*, exactly on a par with the last general election. Yet nationally it was 72.2% (66.1% at the last general election) and, according to the Evening Standard, in comparable Islington it was 70.39% and in south west London 71.98%. So why was turnout in Camden relatively low? Local weather?  Demographics?  Voter registration?  Error in my sums?

*Turnout; 21,128 (postal votes cast) + 74,154 (ballot papers cast) = 95,282 / 145,328 (total Camden electorate) = 65.5%