It's best not to pretend you are based in the UK if you don't have an office here. Therefore I suggest quoting both an 0870 number that redirects to your number abroad, and the actual number abroad too. Then people are free to use whichever is cheaper for them.

Having said that, unless you're in a rather exotic country, it's cheaper to use one of the discount call companies to call abroad than it is to call 0870 numbers.

It must be possible to use a cheaper number than 0845 or 0844 instead of 0870. But whether it's economical is another matter. So you could just quote one of the discount call companies' numbers. e.g. if you are in France, you can tell people to call:
0844 720 2020, 0033 xx xx xx xx...
(calls cost 1p per minute at all times).

"Do you think our image could be effected by using an 0871 number (we would not receive anything for the calls as it goes to the telco to provide the international diversion) if used with our full number?"

Yes.

Both 0870 and 0871 attract bad press - not only in this site.

There are several companies that offer UK geographic numbers that can be used for VoIP; in this way you can offer a (series of) geographic number(s) and have the calls routed very cheaply to suit you.

Even if the Ofcom consultation(s) require a tariff announcement the 087X numbers still look off-putting.