Centrica said a report into bid target Venture Production 'lacks credibility' in a number of areas and that its final offer of 845p will not be increased.On Tuesday, Venture said consulting group Resource Investment Strategy Consultants (RISC) valued it at between 1,066p-1,385p per share. Venture rejected a 845p per share hostile offer from Centrica in July.But Centrica countered today and said it believed the RISC Report and the conclusions drawn from it 'lack credibility in a number of important respects.'The group said teh report relies on overly optimistic assumptions regarding the outlook for gas prices and values Venture's reserves without appropriate regard to risks with their possible development. 'Venture continues to draw valuation comparisons on a 2P multiple basis, as well as to "peer group" share price performance. Centrica's view is that such comparisons are inappropriate,' it added.Centrica said it continues to believe that its offer is "highly attractive" to Venture's shareholders, representing a 46% premium.'Centrica reminds Venture shareholders that the Offer of 845 pence in cash is final and will not be increased, except that Centrica Resources reserves the right to revise and/or increase the Offer if a competitive situation arises,' it said.