(Reuters) - Britain's Just Retirement Group Plc (>> Just Retirement Group PLC) reported a 43 percent jump in first-half operating profit, and said its almost $1 billion purchase of rival Partnership Assurance (>> Partnership Assurance Group PLC) would complete next month.

Just Retirement said total retirement sales of 996.2 million pounds were up more than 50 percent in the first half ended Dec. 31.

Bulk annuity sales - taking on the risk of company defined benefit pension schemes - almost doubled to 701.2 million pounds.

Its solvency capital ratio under new European rules was 133 percent.

Pensions and savings firms have been hit hard by reforms that have removed the obligation for retirees to buy an annuity, a financial product providing income for life that has been a high-margin cornerstone of many companies' businesses.

However, since the announcement of the pension reforms, annuity providers have found new business in the sale of bulk annuities, taking on companies' final salary or defined-benefit schemes.

Partnership Assurance said in a separate statement that total operating profit fell 37.5 percent to 40 million pounds in 2015.

Just Retirement reiterated it would achieve at least 40 million pounds of cost savings after the deal to form JRP Group completes.

Shares in Just Retirement were up 2.910 percent at 137.9 pence at 0851 GMT on Friday on the London Stock Exchange. Partnership Assurance's shares were up 5.35 at 118 pence.

($1 = 0.7004 pounds)

(Reporting by Noor Zainab Hussain in Bengaluru; Editing by Sunil Nair)