4. Operating costs

	2022 £000	2021 £000
Raw materials and consumables (including subcontractor costs)	253,734	215,634
Staff costs (note 6)	86,034	75,630
Other operating charges	33,802	42,836
Amortisation of other intangible assets (note 12)	178	4
Operating lease expense:
– plant and machinery	535	128
– other	118	207
Depreciation (notes 13 and 14):
– owned property, plant and equipment	5,163	4,434
– right-of-use assets	1,702	1,569
Other operating income	(4,584)	(2,658)
Operating costs before non-underlying items	376,682	337,784
Non-underlying items (note 5)	5,424	2,795
	382,106	340,579
Other operating charges include:
Fees payable to the Company's auditor for the audit of the Company's annual accounts	25	25
Fees payable to the Company's auditor for other services:
– the audit of the Company's subsidiaries pursuant to legislation	450	315
– audit-related assurance services	25	25
– other assurance services	–	40

Other operating income mainly represents research and development tax credits.

Fees payable to KPMG LLP and their associates for non-audit services to the Company are not required to be disclosed because the consolidated financial statements are required to disclose such fees on a consolidated basis.

In addition to the non-audit fees above, the Group incurred non-audit fees of £nil (2021: £39,000) in respect of other assurance services provided to its Indian joint venture.

Details of the Group's policy on the use of the auditor for non-audit services, the reason why the auditor was used and how the auditor's independence and objectivity were safeguarded are set out in the audit committee report. No services were performed pursuant to contingent fee arrangements.