"A lot depends on what happens in this environment. If we had political peace and got on with the job of fixing the economy then we may never see the stress. If we have a loss of confidence in the system and the political noise continues, you will see stress," he says.
"It's psychological. If people are not happy then they don't invest, they don't do things, they haven't got confidence to buy things.”
Investec expects to report operating profit slightly behind the prior comparable period, due to high investment spend in its UK specialist bank and changes to accounting policies in the local banking business.
The depreciation of 3% in the average rand against sterling exchange rate over the period would also affect profits, Investec said.
Revenue is expected to be ahead of the previous period, while impairments would remain roughly the same.
Between March 31 and August 31, Investec grew funds under management 13,3% to £137,9bn. Deposits increased 12,7% to £27,1bn over the five-month period, while loans and advances increased 10,5% to £20bn (3,8% on a currency neutral basis).
"We've seen quite a strong moderation in loans and advances compared to the previous year," Koseff says. "We've remained very liquid as a firm. We did defensively increase cash balances in anticipation of the EU referendum."
Investec had increased portfolio impairments in its South African business, but not materially. Impairment charges in SA were expected to be slightly ahead of the prior year, but Koseff says Investec's credit loss ratio remained at the lower end of its target range.
It expected the credit loss ratio - or write-offs as a percentage of total loans - on total average core loans and advances to be between 0,48% and 0,53%. This was lower than the March 2016 and September 2015 figures, respectively, at 0,62% and 0,54%.
Investec's asset management and wealth and investment management businesses were supported by a recovery in equity markets and solid net new inflows, Koseff says.
Asset management posted net inflows of £1,1bn between March and August 2016, with the wealth business attracting £500m over the same period. The businesses respectively had £86,9bn and £50,4bn in funds under management at the end of August, posting increases over the five-month period of 14,8% and 11%, respectively.
