The England and Wales Cricket Board (ECB) faced a one-year-suspension from international cricket and a two million pound fine under the new International Cricket Council (ICC) rules introduced in March if they cited moral obligations and refused to travel.
The ECB did not want to tour but needed specific Government advice not to go to avoid the stiff ICC sanctions.
But Foreign Secretary Jack Straw said the Government did not like the idea of the tour but did not believe the English game should be bankrupted by ICC penalties if it was called off.
In a reply to his conservative counterpart Michael Ancram, Straw wrote: "We fully understand the very difficult decision the ECB has to take, particularly in the light of the ICC's meeting in Auckland in March.
"This meeting appears to have given the ECB a choice between a tour which is difficult to defend on moral grounds and financial penalties which might bankrupt the game.
"I do not like the idea of an England team touring Zimbabwe any more than you do, but I do not believe that the future of English cricket should be put in jeopardy as a result of the failure of others to acknowledge the appalling situation there."
Ancram had suggested a new Government statement might allow the ECB to claim to the ICC they were being pressured into pulling out.
But Straw said the Government had no powers to ban any other sporting organisation from touring Zimbabwe or any other country.
He added in the letter: "There is no evidence that any ministerial statement would be sufficient for the ICC to allow the ECB to postpone the tour.
"In those circumstances, I do not believe it would be right that the British taxpayer should have to carry the financial liability which could flow from cancellation of the tour."
The letter effectively ends any uncertainty about whether the tour will take place and ECB chairman David Morgan insisted that England have no choice but to tour.
Morgan said: "We have to look at what's happening to international cricket at the moment. Sri Lanka are in Zimbabwe and Australia are planning to go. Why shouldn't England go?
"Against that background, the Board members and directors of the ECB we believe that, provided it is safe and secure, this tour has to go ahead.
I do not believe England touring or not touring will make any difference (to the situation in Zimbabwe)."
Morgan believes England would be kicked out of the ICC if they pulled out.
He added: "I think it could well happen for a short period of time, a short but very damaging period."
Straw also pointed out that England were in the same position as Australia.
He told Ancram: "Later this month, the Australian cricket team is due to tour Zimbabwe and you will be aware of the statements made by the Australian Government on this issue.
"Their opposition to the Mugabe regime - like ours - is beyond question. Yet they also believe that decisions about cricket tours must remain with the relevant cricketing authorities."