The LSF have previously walked the line a bit too closely with regards to Bretonia... specifically by getting a bit too close to restricted space in Chester and Newcastle. Bretonia was, predictably, about as happy about that as the LN would be about a BAF in Alaska. If I recall, the LSF officially denied having agents in Bretonia, to which Bretonia replied "good, then we'll assume it's alright to shoot any we catch, since they aren't yours". Chances are that if an LSF is caught snooping around Bretonia, the LSF will rally behind them just as much as the Chinese do when their spies are caught... that is, "We'd never send spies into your country, especially not to commit acts of war! They're not ours, so feel free to execute them for treason!"
"Friends" does not imply "right of passage", much less "full access to restricted space". Do you think the United States would be okay with British soldiers attempting to waltz on into Area 51 without announcing their arrival in the US? Hell no!
EDIT: Come to think about it, I think the LSF trying to fault Bretonia for shooting agents in Bretonian territory would be far more worthy of the exclamation "Are they trying to start a war?" than anything else here. As far as they're concerned, you were caught, sucks to be you.