BT shares jumped 8% on reports last night that it was in talks for a partial sale of its vast Openreach engineering business. Having cut its dividend recently, such discussions would be a convenient fillip for investors. Markets would do well to treat the report with caution, however. Issues such as the Openreach pension fund and its close dependence on BT make disentangling the businesses completely tricky, although it was split in recent years to satisfy calls for it to provide better services to BT's rivals. No doubt there are some big infrastructure investors looking, but a deal seems unlikely. Particularly as directors were buying shares yesterday. If there was a deal in the offing, that would be illegal.