Is our brand too close to a registered trade mark?

Without knowing the actual marks in question, it is difficult to render an opinion, however, there are three basic principles involved - all three are based upon the likelihood of confusion (of the source of the mark) - the first is how close are the marks in reality, the second is what are the fields in which the marks are used - you already indicated such - and the third is the strength of the mark that you might infringe. For example, if the mark is XEROX or GOOGLE, those are extremely strong marks and whatever fields the goods or services are in, there would be an immediate association with the original XEROX and GOOGLE companies. If the marks are not that strong, meaning very well/universally known, and the fields of commerce are different, then you are in a stronger position for not infringing the mark, however, again, it is difficult to truly say without knowing the actual marks.