CARLTON COMMUNICATIONS and GRANADA are in advanced negotiations over a merger that, if successful, would lead to the creation of the only independent television broadcaster in the United Kingdom. The agreement provides for GRENADA shareholders having a 68% stake in the future group and receiving £200 million from CARLTON whose shareholders would own the rest. The new group would be worth some £2.5 to 3 bn. The two groups made a first stab at a rapprochement last February but it failed.