Initial public offering price was 210 pence per share, giving HSS a total market capitalisation of £325m.
The price is at the bottom end of the 210p to 265p range announced last month.
The offer will raise total gross proceeds of £103m for the company and £11m for the selling shareholders assuming no exercise of the over-allotment option, or £22m assuming exercise in full of the over-allotment option. The offer represents 35% of issued shares, if no over-allotment.
Chief executive Chris Davies said: "We are delighted to have completed the IPO process successfully and, with proceeds from the offer enabling us to accelerate our growth, we are excited about our future as a listed business.
"Our focus now will be on executing our proven strategy, and building on our established track record of industry-leading growth and returns on assets, for the benefit of all our shareholders."
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