Sorry - in previous email forgot to include the following code, as the NPE occurs when this routine is called at the addPackage call.
private void readDRLintoPackage(String rulesFile) throws DroolsParserException, IOException, Exception {
Reader source = new InputStreamReader(RulesEngine.class.getResourceAsStream("/" + rulesFile));
PackageBuilder builder = new PackageBuilder();
builder.addPackageFromDrl(source);
Package pkg = builder.getPackage();
rules = RuleBaseFactory.newRuleBase();
rules.addPackage(pkg);
}