<p><span class="m_first-letter m_first-letter--flagged">N</span>ational Grid invested a record &pound;4.5bn in the UK&rsquo;s networks of pipes and wires last year amid an overhaul in the energy system which is spurring the development of a modernised grid.</p> <p>The operator of Britain&rsquo;s high voltage cables and high-pressure gas pipelines said it was&nbsp;starting to see the benefit&nbsp;of its move into the US energy market a decade ago after a rocky start on the other side of the Atlantic.</p>