Auto-enrolment began in October 2012 for the largest firms and will be rolled out in stages to all firms over the next few years.
The firm said inertia would be a strong factor for employees and that the opt-out figure would be lower than the 30 per cent initially predicted.
However, there would still be issues regarding the capacity of pensions providers. Will Aitken, senior defined contribution consultant at Towers Watson, said: "The main concern for 2013 is about capacity. Employers selecting pension providers in the second half of 2013 will find it is no longer a buyers' markets as capacity dries up and providers begin to price accordingly. In addition, the effect of the RDR will see further consolidation in the adviser market and, longer term, possibly in the provider market too."
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Mr Aitken also suggested 2013 could bring an increasing focus on the charges applied to pensions. This would fit in with the industry-wide need for greater transparency.
He said: "There will also be an ever increasing focus on pension charges, from regulators, legislators, employers and employees. Greater transparency in transaction charges and consultancy charging will increase pressure for charges to be split into their component parts, so that members can see how much they are paying for administration, investment management, investment transactions, communications and adviser-related costs respectively.
"Arrangements set up on an 'active member discount' basis, where former employees pay more than current employees will find that model no longer works if 'pot follow member' takes off as seems likely."

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