It would be fair to make a cautionary statement here--I think there is a tendency to proclaim certainty about things that are less-than-fully-supported biblically. In my last few years of school, I attended a school affiliated with a "Fundamental, Independent, KJV-only" type of church. They were very certain about many things--women should not wear pants (trousers, to you in the UK), rock music in any form is evil, going to the cinema to see movies is evil (though maybe watching videos was ok--this was a few years before DVDs). Christians don't drink, smoke, or chew, and don't hang out with those who do (unless one is witnessing to them, which wouldn't technically be hanging out).
In truth, many of their prohibitions had little biblical support. They would say that rock music is the world's music, rooted in rebellion. Some would say that the beat of rock music is too heavy, that the heavy rhythm is carnal and sensual. The problem is, these are arbitrary categories--where does the Bible say anything about any kind of "world's music"? Where does the Bible prohibit music with a heavy rhythm? The Bible does prohibit a man to wear feminine things and vice-versa, but what does that mean? In the times of the New Testament, the normal clothing of men and women were very similar. Why are pants or trousers strictly men's clothing? What about in colder climates, where women wear trouser-like pieces of clothing? What about cultures where women's clothing may include something similar to trousers? On the other hand, should men not wear kilts, because they are too much like skirts?
I could go on, I suppose, but maybe I've made my point--we need to be careful of forbidding things about which the Bible does not explicitly forbid.
Saying that, while acknowledging that grace may be wise in some things where clear commands and limits are not given, the worship of uncertainty as many postmoderns practice is like being eaten by the dragon while avoiding the whirlpool. The Bible makes many things very plain, and these things are not up for dispute. In the Ten Commandments, things like theft and murder and lying and adultery are shown to be wrong. Worshiping other gods is wrong. Any sexual act between anyone other than a man and woman married to each other is called sin.
We did not make the rules, we were not given the power to veto or remake the rules, and we violate the rules at our own peril. And finally, if we go up against the One who made the rules, we may be sure only of certain defeat and punishment.
There is room for flexibility in many things, but there are things hard and fast, things about which there cannot be compromise. To say that we must doubt those things, doubt that God has forbidden us to do those things, is to echo the words of the serpent, “Did God really say?”
En Passant: a work of not-so-popular theology (Kindle Locations 477-496).