the issue was and still is: if a continental dealer is supposed to sell let's say 100 bikes/year and sees 15 british bikes/year imported to "his" territory this dealer is not really happy - and I know at least 3 German examples for just about those figures

But this is quite dangerous territory with respect to Art. 101
Treaty on the Functioning of the European Union and the respective European national laws on competition:
"The following shall be prohibited as incompatible with the internal market: all agreements between undertakings, decisions by associations of undertakings and concerted practices which may affect trade between Member States and which have as their object or effect the prevention, restriction or distortion of competition within the internal market, and in particular those which:
(a) directly or indirectly fix purchase or selling prices or any other trading conditions;
(b) limit or control production, markets, technical development, or investment;
(c) share markets or sources of supply;
(d) apply dissimilar conditions to equivalent transactions with other trading parties, thereby placing them at a competitive disadvantage;
(e) make the conclusion of contracts subject to acceptance by the other parties of supplementary obligations which, by their nature or according to commercial usage, have no connection with the subject of such contracts.
..."
So there is no legal way to prevent UK dealers to sell to continental customers or those customers to buy from UK dealers except bringing UK prices to continentl level

Since the US Supreme Court
changed his mind about minimum resale prices in 2007 US companies are
under close watch in the EC anyway for their respect of EC competition laws.
Garmin alone had to pay 2,5 mio Eur in 2010 for its "kickback scheme" (Garmin reimbursed online traders if they stopped selling under Garmins MSRP, maybe legal under US law, evidently illegal under EC law).
So H-D has to be very, very carefull with its measures to discourage UK dealers to sell to continental customers ...