A primer - after 20 minutes googling -
The UK had already applied to join the EEC in 1969. Both parties in the 1970 GE had stuff to say about negotiations. The Conservative Manifesto said:
"If we can negotiate the right terms, we believe that it would be in the long-term interest of the British people for Britain to join the European Economic Community, and that it would make a major contribution to both the prosperity and the security of our country. The opportunities are immense. Economic growth and a higher standard of living would result from having a larger market.
But we must also recognise the obstacles. There would be short-term disadvantages in Britain going into the European Economic Community which must be weighed against the long-term benefits. Obviously there is a price we would not be prepared to pay. Only when we negotiate will it be possible to determine whether the balance is a fair one, and in the interests of Britain.
Our sole commitment is to negotiate; no more, no less. As the negotiations proceed we will report regularly through Parliament to the country.
A Conservative Government would not be prepared to recommend to Parliament, nor would Members of Parliament approve, a settlement which was unequal or unfair. In making this judgement, Ministers and Members will listen to the views of their constituents and have in mind, as is natural and legitimate, primarily the effect of entry upon the standard of living of the individual citizens whom they represent."
And, in wikipedia - you don't have to rely on Daily Mail propaganda and lies -
"The question of sovereignty was discussed at the time in an official Foreign and Commonwealth Office document. It listed among "Areas of policy in which parliamentary freedom to legislate will be affected by entry into the European Communities": Customs duties, Agriculture, Free movement of labour, services and capital, Transport, and Social Security for migrant workers. The document concluded (paragraph 26) that it was advisable to put the considerations of influence and power before those of formal sovereignty".