This is a preprint of a study by a large group of UK researchers.  One striking finding is that hypertension is not, in fact, a significant co-morbidity for serious illness and death, it rather seems to be a proxy for age, which is a factor (something we wondered about previously).   From the paper:

There was no association between hypertension (defined as a recorded diagnosis, or high blood pressure at the last measurement) and outcome (HR 0.95, 0.89-1.01). However, in sensitivity analyses, diagnosed hypertension was associated with slightly increased risk (HR 1.07, 1.00-1.15) while high blood pressure (≥140/90 mmHg) at the most recent measurement was associated with lower risk (HR 0.61, 0.56-0.67).

This chart below the fold summarizes the findings:

(Thanks to Eric Winsberg for the pointer.)