Complaints about investment bonds offering unit linked guarantees rose by a third over the past year, according the latest data from the Financial Ombudsman Service (FOS).

Between April and December 2009, 1,995 complaints were reported to FOS about the products, compared to 1,497 just a year earlier.

The rise in complaints coincides with an increase in the marketing activity by some of the companies offering investment products with unit-linked guarantees in the UK.

Unit linked guaranteed products are designed to protect in the initial capital amount invested provided the investor holds the portfolio for the full term of the guarantee without taking withdrawals.

Investment gains are locked in on a regular basis from one year to five years depending on the provider and the type of product. Investment complaints as a whole nudged up slightly over the period measured.

There were 10,488 investment complaints in total between April and December 2009, up from 7,945 the same period in 2008.

Non-cash ISAs accounted for 1,099 of these, up from 776 the previous year. Other sources of complaints included portfolio management, mortgage endowments, whole of life policies and ‘other’ investments.