Reuters: Britain must get tough with major oil firms that prevent smaller producers from getting access to platforms and pipelines, or risk leaving as much as $500 billion worth of oil in the ground, North Sea oil companies say. Output from the North Sea has been in steep decline as mature fields are exhausted and global firms such as BP and Shell focus on more promising projects elsewhere. But there is still oil under the sea bed that a host of smaller operators is keen to extract, and Britain's cash-strapped...