A BOOM in oil and gas exploration activity in response to soaring energy prices is making it increasingly hard for smaller independent firms to get access to rigs in the North Sea, according to a Scottish specialist.

Shares in Plexus Holdings plunged 11percent after the Aberdeen-based services firm said sales of its wellhead technology would be affected this year by delays in getting projects started.

Small independent exploration and production firms provide a key market for the specialised sealant technology developed by Plexus for use in oil and gas wells.

However, with rigs being shifted to drill plum prospects overseas independents have been finding it harder to get them for use off Scotland, or had to accept big increases in rental rates.

While the rig shortage will impact on Plexus in the current year, the company said it expected to benefit from future increases in rig availability. The company has continued to win contracts in specialised areas such as high pressure and high temperature wells.

It expects to be a beneficiary of the trend for oil and gas companies to drill increasingly challenging environments as they try to meet booming demand.

Shares in the company slipped 11p to 87.5p. That compares with an issue price of 75p when Plexus floated on the Alternative Investment Market last December.