Further to the very astute response above, it is no longer possible to get reputable installers of electric heating boilers. The carbon rating of these items is too high and they are generally frowned upon within the trade (i dont even think you can get them anymore without importing them). They take forever to heat up and wear elements out every 18-24 months. Most modern houses have limits on the incomming consumer unit which will not allow the electical capacity needed to power them.
If Gas is not an option, have you considered oil (it would need a tank in either a yard or garden), but is actually become more reasonable in recent years due to the riduculous price hike in gas.