Image copyright RMT Image caption The union said the strike was "rock solid"

Rail workers on South Western Railway (SWR) have begun a three-day strike over the role of guards on trains.

Their union the RMT said the walkout, from 00:01 BST on Friday until 23:59 on Sunday, would cause "serious disruption".

SWR said it had planned to run about two-thirds of normal services on Friday and half of its usual weekend services.

The firm said its network was "running well" while the union said the strike was "rock solid".

The walkout is the sixth of eight planned strikes across the summer - the previous five were all for 24 hours.

'Utter contempt'

The RMT (the National Union of Rail, Maritime and Transport Workers) is asking for a guarantee of guards on trains and a halt to the "rolling out of driver-only operation".

SWR said it would roster guards on all services but trains could still operate in "exceptional circumstances" if no guard was available.

RMT general secretary Mick Cash accused the firm of "refusing to engage in serious talks".

He said SWR had treated the union with "utter contempt" by appointing negotiators with no authority to reach a settlement.

Image caption South Western Railway said services would be "much busier than normal"

The firm said it was focused on finding a way to resolve the dispute.

It said services on the final weekend of the summer holidays would be "much busier than normal".

A spokesman said extra capacity had been laid on for passengers travelling to the Bournemouth Air Festival, as well as between Salisbury and Yeovil.

The strike affects routes in Berkshire, Bristol, Devon, Dorset, Hampshire, London, Somerset, Surrey and Wiltshire.

The Isle of Wight, also served by SWR, is unaffected.

The three-day walkout is the joint longest in the two-year dispute over guards, after RMT members on Southern Railway stopped work for three out of five planned strike days in August 2016.

Further strikes on SWR are planned on 8 and 15 September.